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 楼主| 发表于 1/4/2015 22:27:00 | 显示全部楼层
Recommended Intakes


Intake recommendations for calcium and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences) [1]. DRI is the general term for a set of reference values used for planning and assessing the nutrient intakes of healthy people. These values, which vary by age and gender, include:
Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals.
Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
Estimated Average Requirement (EAR): average daily level of intake estimated to meet the requirements of 50% of healthy individuals. It is usually used to assess the adequacy of nutrient intakes in populations but not individuals.
Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects [1].
The FNB established RDAs for the amounts of calcium required for bone health and to maintain adequate rates of calcium retention in healthy people. They are listed in Table 1 in milligrams (mg) per day.
Table 1: Recommended Dietary Allowances (RDAs) for Calcium [1]
Age        Male        Female        Pregnant        Lactating
0–6 months*        200 mg        200 mg                  
7–12 months*        260 mg        260 mg                  
1–3 years        700 mg        700 mg                  
4–8 years        1,000 mg        1,000 mg                  
9–13 years        1,300 mg        1,300 mg                  
14–18 years        1,300 mg        1,300 mg        1,300 mg        1,300 mg
19–50 years        1,000 mg        1,000 mg        1,000 mg        1,000 mg
51–70 years        1,000 mg        1,200 mg                  
71+ years        1,200 mg        1,200 mg                  
* Adequate Intake (AI)

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 楼主| 发表于 1/4/2015 22:37:23 | 显示全部楼层
Sources of Calcium


Food
Milk, yogurt, and cheese are rich natural sources of calcium and are the major food contributors of this nutrient to people in the United States [1]. Nondairy sources include vegetables, such as Chinese cabbage, kale, and broccoli. Spinach provides calcium, but its bioavailability is poor. Most grains do not have high amounts of calcium unless they are fortified; however, they contribute calcium to the diet because they contain small amounts of calcium and people consume them frequently. Foods fortified with calcium include many fruit juices and drinks, tofu, and cereals. Selected food sources of calcium are listed in Table 2.
Table 2: Selected Food Sources of Calcium [2]
Food        Milligrams (mg)
per serving        Percent DV*
Yogurt, plain, low fat, 8 ounces        415        42
Mozzarella, part skim, 1.5 ounces        333        33
Sardines, canned in oil, with bones, 3 ounces        325        33
Yogurt, fruit, low fat, 8 ounces        313–384        31–38
Cheddar cheese, 1.5 ounces        307        31
Milk, nonfat, 8 ounces**        299        30
Soymilk, calcium-fortified, 8 ounces        299        30
Milk, reduced-fat (2% milk fat), 8 ounces        293        29
Milk, buttermilk, lowfat, 8 ounces        284        28
Milk, whole (3.25% milk fat), 8 ounces        276        28
Orange juice, calcium-fortified, 6 ounces        261        26
Tofu, firm, made with calcium sulfate, ½ cup***        253        25
Salmon, pink, canned, solids with bone, 3 ounces        181        18
Cottage cheese, 1% milk fat, 1 cup        138        14
Tofu, soft, made with calcium sulfate, ½ cup***        138        14
Ready-to-eat cereal, calcium-fortified, 1 cup        100–1,000        10–100
Frozen yogurt, vanilla, soft serve, ½ cup        103        10
Turnip greens, fresh, boiled, ½ cup        99        10
Kale, raw, chopped, 1 cup        100        10
Kale, fresh, cooked, 1 cup        94        9
Ice cream, vanilla, ½ cup        84        8
Chinese cabbage, bok choi, raw, shredded, 1 cup        74        7
Bread, white, 1 slice        73        7
Pudding, chocolate, ready to eat, refrigerated, 4 ounces        55        6
Tortilla, corn, ready-to-bake/fry, one 6" diameter        46        5
Tortilla, flour, ready-to-bake/fry, one 6" diameter        32        3
Sour cream, reduced fat, cultured, 2 tablespoons        31        3
Bread, whole-wheat, 1 slice        30        3
Broccoli, raw, ½ cup        21        2
Cheese, cream, regular, 1 tablespoon        14        1
* DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration to help consumers compare the nutrient contents among products within the context of a total daily diet. The DV for calcium is 1,000 mg for adults and children aged 4 years and older. Foods providing 20% of more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet. The U.S. Department of Agriculture’s (USDA’s) Nutrient Databaseexternal link icon Web site lists the nutrient content of many foods and provides comprehensive list of foods containing calcium arranged by nutrient content and by food name.
** Calcium content varies slightly by fat content; the more fat, the less calcium the food contains.
*** Calcium content is for tofu processed with a calcium salt. Tofu processed with other salts does not provide significant amounts of calcium.
In its food guidance system, MyPlate, the U.S. Department of Agriculture recommends that persons aged 9 years and older eat 3 cups of foods from the milk group per day [3]. A cup is equal to 1 cup (8 ounces) of milk, 1 cup of yogurt, 1.5 ounces of natural cheese (such as Cheddar), or 2 ounces of processed cheese (such as American).
Dietary supplements
The two main forms of calcium in supplements are carbonate and citrate. Calcium carbonate is more commonly available and is both inexpensive and convenient. Due to its dependence on stomach acid for absorption, calcium carbonate is absorbed most efficiently when taken with food, whereas calcium citrate is absorbed equally well when taken with or without food [4]. Calcium citrate is also useful for people with achlorhydria, inflammatory bowel disease, or absorption disorders [1]. Other calcium forms in supplements or fortified foods include gluconate, lactate, and phosphate. Calcium citrate malate is a well-absorbed form of calcium found in some fortified juices [5].
Calcium supplements contain varying amounts of elemental calcium. For example, calcium carbonate is 40% calcium by weight, whereas calcium citrate is 21% calcium. Fortunately, elemental calcium is listed in the Supplement Facts panel, so consumers do not need to calculate the amount of calcium supplied by various forms of calcium supplements.
The percentage of calcium absorbed depends on the total amount of elemental calcium consumed at one time; as the amount increases, the percentage absorption decreases. Absorption is highest in doses ≤500 mg [1]. So, for example, one who takes 1,000 mg/day of calcium from supplements might split the dose and take 500 mg at two separate times during the day.
Some individuals who take calcium supplements might experience gastrointestinal side effects including gas, bloating, constipation, or a combination of these symptoms. Calcium carbonate appears to cause more of these side effects than calcium citrate [1], so consideration of the form of calcium supplement is warranted if these side effects are reported. Other strategies to alleviate symptoms include spreading out the calcium dose throughout the day and/or taking the supplement with meals.
Medicines
Because of its ability to neutralize stomach acid, calcium carbonate is found in some over-the-counter antacid products, such as Tums® and Rolaids®. Depending on its strength, each chewable pill or softchew provides 200 to 400 mg of elemental calcium. As noted above, calcium carbonate is an acceptable form of supplemental calcium, especially for individuals who have normal levels of stomach acid.
Calcium Intakes and Status


In the United States, estimated calcium intakes from both food and dietary supplements are provided by the National Health and Nutrition Examination Survey (NHANES), 2003–2006 [6]. Mean dietary calcium intakes for males aged 1 year and older ranged from 871 to 1,266 mg/day depending on life stage group; for females the range was 748 to 968 mg/day. Groups with mean intakes falling below their respective EAR—and thus with a prevalence of inadequacy in excess of 50%—include boys and girls aged 9–13 years, girls aged 14–18 years, women aged 51–70 years, and both men and women older than 70 years [1,6]. Overall, females are less likely than males to get adequate amounts of calcium from food [7].
About 43% of the U.S. population (including almost 70% of older women) uses dietary supplements containing calcium, increasing calcium intakes by about 330 mg/day among supplement users [1,6]. According to NHANES 2003–2006 data, mean total calcium intakes from foods and supplements ranged from 918 to 1,296 mg/day for people aged 1 year and older [6]. When considering total calcium intakes, calcium inadequacy remains a concern for several age groups. These include females aged 4 years and older—particularly adolescent girls—and males aged 9 to 18 years and older than 51 years [1,8]. At the other end of the spectrum, some older women likely exceed the UL when calcium intakes from both food and supplements are included [1].
Not all calcium consumed is actually absorbed in the gut. Humans absorb about 30% of the calcium in foods, but this varies depending upon the type of food consumed [1]. Other factors also affect calcium absorption including the following:
Amount consumed: the efficiency of absorption decreases as calcium intake increases [1].
Age and life stage: net calcium absorption is as high as 60% in infants and young children, who need substantial amounts of the mineral to build bone [1,9]. Absorption decreases to 15%–20% in adulthood (though it is increased during pregnancy) and continues to decrease as people age; compared with younger adults, recommended calcium intakes are higher for females older than 50 years and for both males and females older than 70 years [1,9,10].
Vitamin D intake: this nutrient, obtained from food and produced by skin when exposed to sunlight of sufficient intensity, improves calcium absorption [1].
Other components in food: phytic acid and oxalic acid, found naturally in some plants, bind to calcium and can inhibit its absorption. Foods with high levels of oxalic acid include spinach, collard greens, sweet potatoes, rhubarb, and beans. Among the foods high in phytic acid are fiber-containing whole-grain products and wheat bran, beans, seeds, nuts, and soy isolates [1]. The extent to which these compounds affect calcium absorption varies. Research shows, for example, that eating spinach and milk at the same time reduces absorption of the calcium in milk [11]. In contrast, wheat products (with the exception of wheat bran) do not appear to lower calcium absorption [12]. For people who eat a variety of foods, these interactions probably have little or no nutritional consequence and, furthermore, are accounted for in the overall calcium DRIs, which factor in differences in absorption of calcium in mixed diets.
Some absorbed calcium is eliminated from the body in urine, feces, and sweat. This amount is affected by such factors as the following:
Sodium and protein intakes: high sodium intake increases urinary calcium excretion [13,14]. High protein intake also increases calcium excretion and was therefore thought to negatively affect calcium status [13,14]. However, more recent research suggests that high protein intake also increases intestinal calcium absorption, effectively offsetting its effect on calcium excretion, so whole body calcium retention remains unchanged [15].
Caffeine intake: this stimulant in coffee and tea can modestly increase calcium excretion and reduce absorption [16]. One cup of regular brewed coffee, for example, causes a loss of only 2–3 mg of calcium [14]. Moderate caffeine consumption (1 cup of coffee or 2 cups of tea per day) in young women has no negative effects on bone [17].
Alcohol intake: alcohol intake can affect calcium status by reducing its absorption [18] and by inhibiting enzymes in the liver that help convert vitamin D to its active form [19]. However, the amount of alcohol required to affect calcium status and whether moderate alcohol consumption is helpful or harmful to bone is unknown.
Phosphorus intake: the effect of this mineral on calcium excretion is minimal. Several observational studies suggest that consumption of carbonated soft drinks with high levels of phosphate is associated with reduced bone mass and increased fracture risk. However, the effect is probably due to replacing milk with soda rather than the phosphorus itself [20,21].
Fruit and vegetable intakes: metabolic acids produced by diets high in protein and cereal grains increase calcium excretion [22]. Fruits and vegetables, when metabolized, shift the acid/base balance of the body towards the alkaline by producing bicarbonate, which reduces calcium excretion. However, it is unclear if consuming more fruits and vegetables affects bone mineral density. These foods, in addition to reducing calcium excretion, could possibly reduce calcium absorption from the gut and therefore have no net effect on calcium balance.


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 楼主| 发表于 1/4/2015 22:54:53 | 显示全部楼层
Calcium Deficiency


Inadequate intakes of dietary calcium from food and supplements produce no obvious symptoms in the short term. Circulating blood levels of calcium are tightly regulated. Hypocalcemia results primarily from medical problems or treatments, including renal failure, surgical removal of the stomach, and use of certain medications (such as diuretics). Symptoms of hypocalcemia include numbness and tingling in the fingers, muscle cramps, convulsions, lethargy, poor appetite, and abnormal heart rhythms [23]. If left untreated, calcium deficiency leads to death.
Over the long term, inadequate calcium intake causes osteopenia which if untreated can lead to osteoporosis. The risk of bone fractures also increases, especially in older individuals [1]. Calcium deficiency can also cause rickets, though it is more commonly associated with vitamin D deficiency [1].


Groups at Risk of Calcium Inadequacy


Although frank calcium deficiency is uncommon, dietary intakes of the nutrient below recommended levels might have negative health consequences over the long term. The following groups are among those most likely to need extra calcium.


Postmenopausal women
Menopause leads to bone loss because decreases in estrogen production both increase bone resorption and decrease calcium absorption [10,24,25]. Annual decreases in bone mass of 3%–5% per year frequently occur in the first years of menopause, but the decreases are typically less than 1% per year after age 65 [26]. Increased calcium intakes during menopause do not completely offset this bone loss [27,28]. Hormone replacement therapy (HRT) with estrogen and progesterone helps increase calcium levels and prevent osteoporosis and fractures. Estrogen therapy restores postmenopausal bone remodeling to the same levels as at premenopause, leading to lower rates of bone loss [24], perhaps in part by increasing calcium absorption in the gut. Several medical groups and professional societies support the use of HRT as an option for women who are at increased risk of osteoporosis or fractures [29-31]. Such women should discuss this matter with their health care providers. In addition, consuming adequate amounts of calcium in the diet might help slow the rate of bone loss in all women.


Amenorrheic women and the female athlete triad


Amenorrhea, the condition in which menstrual periods stop or fail to initiate in women of childbearing age, results from reduced circulating estrogen levels that, in turn, have a negative effect on calcium balance. Amenorrheic women with anorexia nervosa have decreased calcium absorption and higher urinary calcium excretion rates, as well as a lower rate of bone formation than healthy women [32]. The "female athlete triad" refers to the combination of disordered eating, amenorrhea, and osteoporosis. Exercise-induced amenorrhea generally results in decreased bone mass [33,34]. In female athletes and active women in the military, low bone-mineral density, menstrual irregularities, certain dietary patterns, and a history of prior stress fractures are associated with an increased risk of future stress fractures [35]. Such women should be advised to consume adequate amounts of calcium and vitamin D. Supplements of these nutrients have been shown to reduce the risk of stress fractures in female Navy recruits during basic training [36].


Individuals with lactose intolerance or cow's milk allergy


Lactose intolerance refers to symptoms (such as bloating, flatulence, and diarrhea) that occur when one consumes more lactose, the naturally occurring sugar in milk, than the enzyme lactase produced by the small intestine can hydrolyze into its component monosaccharides, glucose and galactose [37]. The symptoms vary, depending on the amount of lactose consumed, history of consumption of lactose-containing foods, and type of meal. Although the prevalence of lactose intolerance is difficult to discern [38], some reports suggest that approximately 25% of U.S. adults have a limited ability to digest lactose, including 85% of Asians, 50% of African Americans, and 10% of Caucasians [39,40,41].


Lactose-intolerant individuals are at risk of calcium inadequacy if they avoid dairy products [1,38,39]. Research suggests that most people with lactose intolerance can consume up to 12 grams of lactose, such as that present in 8 ounces of milk, with minimal or no symptoms, especially if consumed with other foods; larger amounts can frequently be consumed if spread over the day and eaten with other foods [1,38,39]. Other options to reduce symptoms include eating low-lactose dairy products including aged cheeses (such as Cheddar and Swiss), yogurt, or lactose-reduced or lactose-free milk [1,38,39]. Some studies have examined whether it is possible to induce adaptation by consuming incremental lactose loads over a period of time [42,43], but the evidence in support of this strategy is inconsistent [38].


Cow's milk allergy is less common than lactose intolerance, affecting 0.6% to 0.9% of the population [44]. People with this condition are unable to consume any products containing cow's milk proteins and are therefore at higher risk of obtaining insufficient calcium.


To ensure adequate calcium intakes, lactose-intolerant individuals and those with cow's milk allergy can choose nondairy food sources of the nutrient (such as kale, bok choy, Chinese cabbage, broccoli, collards and fortified foods) or take a calcium supplement.


Vegetarians


Vegetarians might absorb less calcium than omnivores because they consume more plant products containing oxalic and phytic acids [1]. Lacto-ovo vegetarians (who consume eggs and dairy) and nonvegetarians have similar calcium intakes [45,46]. However, vegans, who eat no animal products and ovo-vegetarians (who eat eggs but no dairy products), might not obtain sufficient calcium because of their avoidance of dairy foods [47,48]. In the Oxford cohort of the European Prospective Investigation into Cancer and Nutrition, bone fracture risk was similar in meat eaters, fish eaters and vegetarians, but higher in vegans, likely due to their lower mean calcium intake [49]. It is difficult to assess the impact of vegetarian diets on calcium status because of the wide variety of eating practices and thus should be considered on a case by case basis.

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 楼主| 发表于 1/5/2015 01:10:28 | 显示全部楼层
Calcium and Health


Many claims are made about calcium's potential benefits in health promotion and disease prevention and treatment. This section focuses on several areas in which calcium is or might be involved: bone health and osteoporosis; cardiovascular disease; blood pressure regulation and hypertension; cancers of the colon, rectum, and prostate; kidney stones; and weight management.


Bone health and osteoporosis
Bones increase in size and mass during periods of growth in childhood and adolescence, reaching peak bone mass around age 30. The greater the peak bone mass, the longer one can delay serious bone loss with increasing age. Everyone should therefore consume adequate amounts of calcium and vitamin D throughout childhood, adolescence, and early adulthood. Osteoporosis, a disorder characterized by porous and fragile bones, is a serious public health problem for more than 10 million U.S. adults, 80% of whom are women. (Another 34 million have osteopenia, or low bone mass, which precedes osteoporosis.) Osteoporosis is most associated with fractures of the hip, vertebrae, wrist, pelvis, ribs, and other bones [50]. An estimated 1.5 million fractures occur each year in the United States due to osteoporosis [51]. Supplementation with calcium plus vitamin D has been shown to be effective in reducing fractures and falls (which can cause fractures) in institutionalized older adults [52,53].


When calcium intake is low or ingested calcium is poorly absorbed, bone breakdown occurs as the body uses its stored calcium to maintain normal biological functions. Bone loss also occurs as part of the normal aging process, particularly in postmenopausal women due to decreased amounts of estrogen. Many factors increase the risk of developing osteoporosis, including being female, thin, inactive, or of advanced age; smoking cigarettes; drinking excessive amounts of alcohol; and having a family history of osteoporosis [54].


Various bone mineral density (BMD) tests are available. The T-score from these tests compares an individual's BMD to an optimal BMD (that of a healthy 30-year old adult). A T-score of -1.0 or above indicates normal bone density, -1.0 to -2.5 indicates low bone mass (osteopenia), and lower than -2.5 indicates osteoporosis [55]. Although osteoporosis affects individuals of all races, ethnicities, and both genders, women are at highest risk because their skeletons are smaller than those of men and because of the accelerated bone loss that accompanies menopause. Regular exercise and adequate intakes of calcium and vitamin D are critical to the development and maintenance of healthy bones throughout the life cycle. Both weight-bearing exercises (such as walking, running, and activities where one's feet leave and hit the ground and work against gravity) and resistance exercises (such as calisthenics and that involve weights) support bone health.


In 1993, the U.S. Food and Drug Administration authorized a health claim related to calcium and osteoporosis for foods and supplements [56]. In January 2010, this health claim was expanded to include vitamin D. Model health claims include the following: "Adequate calcium throughout life, as part of a well-balanced diet, may reduce the risk of osteoporosis" and "Adequate calcium and vitamin D as part of a healthful diet, along with physical activity, may reduce the risk of osteoporosis in later life" [56].


Cancer of the colon and rectum
Data from observational and experimental studies on the potential role of calcium in preventing colorectal cancer, though somewhat inconsistent, are highly suggestive of a protective effect [1]. Several studies have found that higher intakes of calcium from foods (low-fat dairy sources) and/or supplements are associated with a decreased risk of colon cancer [57-60]. In a follow-up study to the Calcium Polyp Prevention Study, supplementation with calcium carbonate led to reductions in the risk of adenoma (a nonmalignant tumor) in the colon, a precursor to cancer [61,62], even as long as 5 years after the subjects stopped taking the supplement [63]. In two large prospective epidemiological trials, men and women who consumed 700–800 mg per day of calcium had a 40%–50% lower risk of developing left-side colon cancer [64]. But other observational studies have found the associations to be inconclusive [60,65,66].


In the Women's Health Initiative, a clinical trial involving 36,282 postmenopausal women, daily supplementation with 1,000 mg of calcium and 400 International Units (IU) of vitamin D3 for 7 years produced no significant differences in the risk of invasive colorectal cancer compared to placebo [67]. The authors of a Cochrane systematic review concluded that calcium supplementation might moderately help prevent colorectal adenomas, but there is not enough evidence to recommend routine use of calcium supplements to prevent colorectal cancer [68]. Given the long latency period for colon cancer development, long-term studies are needed to fully understand whether calcium intakes affect colorectal cancer risk.


Cancer of the prostate
Several epidemiological studies have found an association between high intakes of calcium, dairy foods or both and an increased risk of developing prostate cancer [69-75]. However, others have found only a weak relationship, no relationship, or a negative association between calcium intake and prostate cancer risk [76-79]. The authors of a meta-analysis of prospective studies concluded that high intakes of dairy products and calcium might slightly increase prostate cancer risk [80].


Interpretation of the available evidence is complicated by the difficulty in separating the effects of dairy products from that of calcium. But overall, results from observational studies suggest that total calcium intakes >1,500 mg/day or >2,000 mg/day may be associated with increased prostate cancer risk (particularly advanced and metastatic cancer) compared with lower amounts of calcium (500–1,000 mg/day [1,81]. Additional research is needed to clarify the effects of calcium and/or dairy products on prostate cancer risk and elucidate potential biological mechanisms.


Cardiovascular disease
Calcium has been proposed to help reduce cardiovascular disease (CVD) risk by decreasing intestinal absorption of lipids(脂質), increasing lipid excretion, lowering cholesterol (膽固醇)levels in the blood, and promoting calcium influx into cells [1]. However, data from prospective studies of calcium's effects on CVD risk are inconsistent, and whether dietary calcium has different effects on the cardiovascular system than supplemental calcium is not clear. In the Iowa Women's Health Study, higher calcium intake from diet and/or supplements was associated with reduced ischemic heart disease mortality in postmenopausal women [82]. Conversely, in a cohort of older Swedish women, both total and dietary calcium intakes of 1,400 mg/day and higher were associated with higher rates of death from CVD and ischemic heart disease than intakes of 600–1,000 mg/day [83]. Other prospective studies have shown no significant associations between calcium intake and cardiac events or cardiovascular mortality [81]. Data for stroke are mixed, with some studies linking higher calcium intakes to lower risk of stroke, and others finding no associations or trends in the opposite direction [81,83].


Several recent studies have raised concerns about the safety of calcium supplements with respect to CVD. Xiao and colleagues reported that men who took more than 1,000 mg/day supplemental calcium had a 20% higher risk of total CVD death than men who did not take supplemental calcium, but supplemental calcium intake in women was unrelated to CVD mortality [84]. In a reanalysis of data from the Women's Health Initiative (WHI), Bolland and colleagues found that calcium supplements (1,000 mg/day) taken with or without vitamin D (400 IU/day) increased the risk of cardiovascular events in women who were not taking calcium supplements when they entered the study [85]. Other studies have also shown that people who take calcium supplements have an increased risk of cardiovascular events, including myocardial infarction [86-88] and coronary heart disease [89]. However, the authors of a 2013 analysis of WHI clinical trial data combined with data from the WHI observational study, which followed over 93,000 postmenopausal women for about 8 years, concluded that "there was little evidence for an adverse influence of calcium and vitamin D supplementation on the risk for myocardial infarction, coronary heart disease, total heart disease, stroke or total cardiovascular disease" [90].


Scientists hypothesize that any adverse effects of calcium supplementation on the cardiovascular system could be mediated through hypercalcemia which can occur when excessively high calcium intakes override normal homeostatic control of serum calcium levels [83]. Hypercalcemia has been associated with increased blood coagulation, vascular calcification, and arterial stiffness, thereby raising CVD risk [84,85,91,92]. High calcium intakes can also increase circulating levels of fibroblast growth factor 23, which is associated with an increased risk of cardiovascular events [83]. Supplemental calcium, in particular, causes an acute increase in serum calcium levels, and some researchers hypothesize that this abrupt change, rather than total calcium load, could be responsible for the observed adverse effects [85].


Many scientists have questioned the strength of the available evidence that links supplemental calcium intake with CVD risk, noting that researchers have only considered CVD outcomes in secondary analyses of trial data and these outcomes have not been the primary endpoint of any calcium supplementation trials to date [91,93]. In their 2012 review of prospective studies and randomized clinical trials, Wang and colleagues concluded that calcium intake from diet or supplements appears to have little or no effect on CVD risk but the available evidence does not allow for a definitive conclusion [91]. The possibility that calcium supplements might harm the cardiovascular system has become a topic of much debate within the scientific community and warrants further investigation.

Blood pressure and hypertension高血壓
Several clinical trials have demonstrated a relationship between increased calcium intakes and both lower blood pressure and risk of hypertension [94-96], although the reductions are inconsistent. In the Women's Health Study, calcium intake was inversely associated with risk of hypertension in middle-aged and older women [97]. However, other studies have found no association between calcium intake and incidence of hypertension [81]. The authors of a systematic review of the effects of calcium supplements for hypertension found any link to be weak at best, largely due to the poor quality of most studies and differences in methodologies [98].


Calcium's effects on blood pressure might depend upon the population being studied. In hypertensive subjects, calcium supplementation appears to lower systolic blood pressure by 2–4 mmHg, whereas in normotensive subjects, calcium appears to have no significant effect on systolic or diastolic blood pressure [81].


Other observational and experimental studies suggest that individuals who eat a vegetarian diet high in minerals (such as calcium, magnesium, and potassium) and fiber and low in fat tend to have lower blood pressure [48,99-102]. The Dietary Approaches to Stop Hypertension (DASH) study was conducted to test the effects of three different eating patterns on blood pressure: a control "typical" American diet; one high in fruits and vegetables; and a third diet high in fruits, vegetables, and low-fat dairy products. The diet containing dairy products resulted in the greatest decrease in blood pressure [103], although the contribution of calcium to this effect was not evaluated. Additional information and sample DASH menu plans are available on the National Heart, Lung, and Blood Institute Web siteexternal link icon.


Kidney stones
Kidney stones in the urinary tract are most commonly composed of calcium oxalate. Some, but not all, studies suggest a positive association between supplemental calcium intake and the risk of kidney stones, and these findings were used as the basis for setting the calcium UL in adults [1]. In the Women's Health Initiative, postmenopausal women who consumed 1,000 mg of supplemental calcium and 400 IU of vitamin D per day for 7 years had a 17% higher risk of kidney stones than subjects taking a placebo [104]. The Nurses' Health Study also showed a positive association between supplemental calcium intake and kidney stone formation [105]. High intakes of dietary calcium, on the other hand, do not appear to cause kidney stones and may actually protect against developing them [1,105-108]. For most individuals, other risk factors for kidney stones, such as high intakes of oxalates from food and low intakes of fluid, probably play a bigger role than calcium intake [109].


Weight management
Several studies have linked higher calcium intakes to lower body weight or less weight gain over time [110-113]. Two explanations have been proposed. First, high calcium intakes might reduce calcium concentrations in fat cells by decreasing the production of parathyroid hormone and the active form of vitamin D. Decreased intracellular calcium concentrations in turn increase fat breakdown and discourage fat accumulation in these cells [112]. Secondly, calcium from food or supplements might bind to small amounts of dietary fat in the digestive tract and prevent its absorption [112,114,115]. Dairy products, in particular, might contain additional components that have even greater effects on body weight than their calcium content alone would suggest [113,116-120].


Despite these findings, the results from clinical trials have been largely negative. For example, dietary supplementation with 1,500 mg/day of calcium (from calcium carbonate) for 2 years was found to have no clinically significant effects on weight in 340 overweight and obese adults as compared with placebo [121]. Three reviews of published studies on calcium from supplements or dairy products on weight management came to similar conclusions [81,122,123]. A meta-analysis of 13 randomized controlled trials published in 2006 concluded that neither calcium supplementation nor increased dairy product consumption had a statistically significant effect on weight reduction [122]. More recently, a 2009 evidence report from the Agency for Healthcare Research and Quality concluded that, overall, clinical trial results do not support an effect of calcium supplementation on weight loss [81]. Also, a 2012 meta-analysis of 29 randomized controlled trials found no benefit of an increased consumption of dairy products on body weight and fat loss in long-term studies [123]. Overall, the results from clinical trials do not support a link between higher calcium intakes and lower body weight or weight loss.

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 楼主| 发表于 1/5/2015 01:22:13 | 显示全部楼层
Health Risks from Excessive Calcium


Excessively high levels of calcium in the blood known as hypercalcemia can cause renal insufficiency, vascular and soft tissue calcification, hypercalciuria (high levels of calcium in the urine) and kidney stones [1]. Although very high calcium intakes have the potential to cause hypercalcemia [83], it is most commonly associated with primary hyperparathyroidism or malignancy [1].


High calcium intake can cause constipation便秘. It might also interfere with the absorption of iron and zinc, though this effect is not well established [1]. High intake of calcium from supplements, but not foods, has been associated with increased risk of kidney stones [1,104,105]. Some evidence links higher calcium intake with increased risk of prostate cancer, but this effect is not well understood, in part because it is challenging to separate the potential effect of dairy products from that of calcium [1]. Some studies also link high calcium intake, particularly from supplements, with increased risk of cardiovascular disease [83-89].


The Tolerable Upper Intake Levels (ULs) for calcium established by the Food and Nutrition Board are listed in Table 3 in milligrams (mg) per day. Getting too much calcium from foods is rare; excess intakes are more likely to be caused by the use of calcium supplements. NHANES data from 2003–2006 indicate that approximately 5% of women older than 50 years have estimated total calcium intakes (from foods and supplements) that exceed the UL by about 300–365 mg [1,6].


Table 3: Tolerable Upper Intake Levels (ULs) for Calcium [1]
Age        Male        Female        Pregnant        Lactating
0–6 months        1,000 mg        1,000 mg                  
7–12 months        1,500 mg        1,500 mg                  
1–8 years        2,500 mg        2,500 mg                  
9–18 years        3,000 mg        3,000 mg        3,000 mg        3,000 mg
19–50 years        2,500 mg        2,500 mg        2,500 mg        2,500 mg
51+ years        2,000 mg        2,000 mg                  


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Interactions with Medications


Calcium supplements have the potential to interact with several types of medications. This section provides a few examples. Individuals taking these medications on a regular basis should discuss their calcium intake with their healthcare providers.


Calcium can decrease absorption of the following drugs when taken together: biphosphonates (to treat osteoporosis), the fluoroquinolone and tetracycline classes of antibiotics, levothyroxine, phenytoin (an anticonvulsant), and tiludronate disodium (to treat Paget's disease) [124-126].


Thiazide-type diuretics can interact with calcium carbonate and vitamin D supplements, increasing the risks of hypercalcemia and hypercalciuria [125].


Both aluminum- and magnesium-containing antacids increase urinary calcium excretion. Mineral oil and stimulant laxatives decrease calcium absorption. Glucocorticoids, such as prednisone, can cause calcium depletion and eventually osteoporosis when they are used for months [125].

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Calcium and Healthful Diets


The federal government's 2010 Dietary Guidelines for Americans notes that "nutrients should come primarily from foods. Foods in nutrient-dense, mostly intact forms contain not only the essential vitamins and minerals that are often contained in nutrient supplements, but also dietary fiber and other naturally occurring substances that may have positive health effects. ...Dietary supplements...may be advantageous in specific situations to increase intake of a specific vitamin or mineral."


For more information about building a healthful diet, refer to the Dietary Guidelines for Americansexternal link icon and the U.S. Department of Agriculture's food guidance system, MyPlateexternal link icon.


The Dietary Guidelines for Americans describes a healthy diet as one that:
Emphasizes a variety of fruits, vegetables, whole grains, and fat-free or low-fat milk and milk products.
Many dairy products, such as milk, cheese, and yogurt, are rich sources of calcium. Some vegetables provide significant amounts of calcium, as do some fortified cereals and juices.


Includes lean meats, poultry, fish, beans, eggs, and nuts.


Tofu made with calcium salts is a good source of calcium (check the label), as are canned sardines and canned salmon with edible bones.


Is low in saturated fats, trans fats, cholesterol, salt (sodium), and added sugars.


Low-fat and nonfat dairy products provide amounts of calcium that are roughly similar to the amounts in their full-fat versions.


Stays within your daily calorie needs.

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Zemel MB, Richards J, Mathis S, Milstead A, Gebhardt L, Silva E. Dairy augmentation of total and central fat loss in obese subjects. Int J Obes 2005;29:391-7. [PubMed abstract]
Zemel MB, Richards J, Milstead A, Campbell P. Effects of calcium and dairy on body composition and weight loss in African-American adults. Obes Res 2005;13:1218-25. [PubMed abstract]
Yanovski JA, Parikh SJ, Yanoff LB, Denkinger BI, Calis KA, Reynolds JC, et al. Effects of calcium supplementation on body weight and adiposity in overweight and obese adults. Ann Intern Med 2009;150:821-829. [PubMed abstract]
Trowman R, Dumville JC, Hahn S, Torgerson DJ. A systematic review of the effects of calcium supplementation on body weight. Br J Nutr 2006;95:1033-8. [PubMed abstract]
Chen M, Pan A, Malik VS, Hu FB. Effects of dairy intake on body weight and fat: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2012;96:735-747. [PubMed abstract]
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Jellin JM, Gregory P, Batz F, Hitchens K. Pharmacist's Letter/Prescriber's Letter Natural Medicines Comprehensive Database. 3rd ed. Stockton, CA: Therapeutic Research Facility, 2000.
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Disclaimer


This fact sheet by the Office of Dietary Supplements provides information that should not take the place of medical advice. We encourage you to talk to your healthcare providers (doctor, registered dietitian, pharmacist, etc.) about your interest in, questions about, or use of dietary supplements and what may be best for your overall health. Any mention in this publication of a specific brand name is not an endorsement of the product.
Reviewed: November 21, 2013

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 楼主| 发表于 1/5/2015 02:36:52 | 显示全部楼层
本帖最后由 郭国汀 于 1/5/2015 02:41 编辑

Calcium: An Important Nutrient that Builds Stronger Bones


Osteoporosis Calcium RequirementsBone is living tissue, constantly renewing itself. Although bone is strong and relatively flexible, everyday wear and tear causes tiny structural defects, much like those that occur in the foundations of a building over time. In our bodies, there are two groups of special cells that perform the work of a “maintenance crew.”  Osteoclasts excavate any areas of damaged or weakened bone and then osteoblasts fill in the crevices with material that hardens to form new bone. This two-part process is called bone remodelling, and the cycle of remodelling is completed every three to four months in a healthy young adult.
As we age, the two groups of cells that form the maintenance crew become less efficient in working together – the osteoclasts remove old bone faster than the osteoblasts are able to rebuild it. In addition, calcium, like many nutrients, is absorbed less effectively as we age. In people who have relatively healthy bones, adequate calcium intake can help the remodelling process stay balanced. Studies of older adults show that adequate calcium intake can slow bone loss and lower the risk of fracture.
For those over 50, Canada’s Food Guide recommends 3 servings of milk and alternatives (2 servings for adults under age 50) – yogurt, cheese, calcium-fortified beverages, puddings, custards, etc. This essentially means that, if you are over 50, you need the equivalent of one good serving of dairy at each meal.
Take your pick:  have a glass of milk (go ahead and have chocolate milk if you prefer), have soup that’s made with milk (like cream of mushroom soup), main courses made with cheese such as lasagna, or have yogurt with fruit for dessert. A 3 cm cube of hard cheese has as much calcium as a cup of milk. Skim milk products provide as much calcium as whole milk with the added advantage of less fat and cholesterol. Dairy products are an excellent source of calcium and are also a good source of protein.
If you are intolerant to dairy products or if you prefer to avoid dairy, there are other alternatives food sources that are high in calcium. These include:
calcium-fortified soy, almond and rice beverages (check the nutrition labels)
calcium-fortified orange juice (check the nutrition labels)
canned salmon or canned sardines. (When you eat the bones that have been softened by the canning process, these foods are excellent sources of calcium.)
Age        Daily Calcium Requirement (this includes your diet and supplements)
19 to 50        1000 mg
50+        1200 mg
pregnant or lactatingwomen 18+        1000 mg

CALCIUM CONTENT OF SOME COMMON FOODS        PORTION        CALCIUM*
Food Product – 250 to 300+ mg Ca
Buttermilk        1 cup/250mL        300 mg
Fortified orange juice        1 cup/250mL        300 mg
Fortified rice or soy beverage        1 cup/250mL        300 mg**
Milk – whole, 2%, 1%, skim, chocolate        1 cup/250mL        300 mg***
Milk, evaporated        1/2 cup/125 mL        367 mg
Milk – powder, dry        1/3 cup/75 mL        270 mg
Yogurt – plain, 1-2% M.F.        3/4 cup/175 mL        332 mg

Food Product – 160 to 249 mg Ca
Almonds, dry roast        1/2 cup/125 mL        186 mg
Beans – white, canned        1 cup/250 mL        191 mg
Cheese – Blue, Brick, Cheddar, Edam, Gouda, Gruyere, Swiss        1 ¼”/3 cm cube        245 mg
Cheese – Mozzarella        1 ¼”/3 cm cube        200 mg
Drinkable yogurt        4/5 cup/200 mL        191 mg
Frozen yogurt, vanilla        1 cup/250 mL        218 mg
Fruit-flavoured yogurt        3/4 cup/175 mL        200 mg
Ice cream cone, vanilla, soft serve        1        232 mg
Kefir (fermented milk drink) – plain        3/4 cup/175 mL        187 mg
Molasses, blackstrap        1 Tbsp/15 mL        180 mg
Salmon, with bones – canned        1/2 can/105 g        240 mg
Sardines, with bones        1/2 can/55 g        200 mg
Soybeans, cooked        1 cup/250 mL        170 mg

Food Product – 125 to 159 mg Ca
Beans – baked, with pork, canned        1 cup/250 mL        129 mg
Beans – navy, soaked, drained, cooked        1 cup/250 mL        126 mg
Collard greens – cooked        1/2 cup/125 mL        133 mg
Cottage cheese, 1 or 2%        1 cup/250 mL        150 mg
Figs, dried        10        150 mg
Instant oatmeal, calcium added        1 pouch/32 g        150 mg
Soy flour        1/2 cup/125 mL        127 mg
Tofu, regular – with calcium sulfate        3 oz/84 g        130 mg

Food Product – 75 to 124 mg Ca
Beans – baked, plain        1 cup/250 mL        86 mg
Beans – great northern, soaked, drained, cooked        1 cup/250 mL        120 mg
Beans – pinto, soaked, drained, cooked        1 cup/250 mL        79 mg
Beet greens – cooked        1/2 cup/125 mL        82 mg
Bok choy, Pak-choi – cooked        1/2 cup/125 mL        84 mg
Bread, white        2 slices        106 mg
Chickpeas (garbanzo beans)        1 cup/250 mL        77 mg
Chili con carne, with beans – canned        1 cup/250 mL        84 mg
Cottage cheese – 2%, 1%        1/2 cup/125 mL        75 mg
Dessert tofu        1/2 cup/100 g        75 mg
Okra – frozen, cooked        1/2 cup/125 mL        89 mg
Processed cheese slices, thin        1        115 mg
Turnip greens – frozen, cooked        1/2 cup/125 mL        104 mg

Food Product – under 75 mg Ca
Artichoke – cooked        1 medium        54 mg
Beans, snap – fresh or frozen, cooked        1/2 cup/125 mL        33 mg
Broccoli – cooked        1/2 cup/125 mL        33 mg
Chinese broccoli (gai lan) – cooked        1/2 cup/125 mL        46 mg
Dandelion greens – cooked        1/2 cup/125 mL        74 mg
Edamame (East Asian dish, baby soybeans in the pod)        1/2 cup/125 mL        52 mg
Fireweed leaves, raw        1/2 cup/125 mL        52 mg
Grapefruit, pink or red        1/2        27 mg
Hummus        1/2 cup/125 mL        50 mg
Kale – cooked        1/2 cup/125 mL        49 mg
Kiwifruit        1        26 mg
Mustard greens – cooked        1/2 cup/125 mL        55 mg
Orange        1 medium        50 mg
Parmesan cheese, grated        1 Tbsp/15 mL        70 mg
Rutabaga (yellow turnip) – cooked        1/2 cup/125 mL        43 mg
Seaweed (agar) – dried        1/2 cup/125 mL        35 mg
Snow peas – cooked        1/2 cup/125 mL        36 mg
Squash (acorn, butternut) – cooked        1/2 cup/125 mL        44 mg
*Approximate values. **Added calcium may settle to the bottom of the container; shake well before drinking. ***Calcium-enriched milk – add 100 mg per serving.
The calcium in soy beverage is absorbed at the rate of 75% of milk. The calcium in some foods such as sesame seeds, rhubarb大黃, Swiss chard唐萵苣,牛皮菜 and spinach is not well absorbed, because of very high oxalate content, which binds the calcium. Therefore these foods have not been included.

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 楼主| 发表于 1/5/2015 02:43:48 | 显示全部楼层
Calcium and Vitamin D: What You Need to Know


Getting enough calcium and vitamin D is essential to building strong, dense bones when you're young and to keeping them strong and healthy as you age. The information included here will help you learn all about calcium and vitamin D - the two most important nutrients for bone health.
What is Calcium and What Does it Do?
How Much Calcium Do You Need?
Sources of Calcium
Calcium Supplements
What is Vitamin D and What Does it Do?
How Much Vitamin D Do You Need?
Sources of Vitamin D
Vitamin D Deficiency: Are You at Risk?
What is Calcium and What Does it Do?


Calcium is a mineral that is necessary for life. In addition to building bones and keeping them healthy, calcium helps our blood clot, nerves send messages and muscles contract . About 99 percent of the calcium in our bodies is in our bones and teeth. Each day, we lose calcium through our skin, nails, hair, sweat, urine and feces, but our bodies cannot produce new calcium.
That’s why it’s important to try to get calcium from the food we eat. When we don’t get enough calcium for our body’s needs, it is taken from our bones.
Too many Americans fall short of getting the amount of calcium they need every day and that can lead to bone loss, low bone density and even broken bones.
How Much Calcium Do You Need?


The amount of calcium you need every day depends on your age and sex.
Women
Age 50 & younger
1,000 mg* daily
Age 51 & older
1,200 mg* daily
Men
Age 70 & younger
1,000 mg* daily
Age 71 & older
1,200 mg* daily
*This includes the total amount of calcium you get from food and supplements.


How Much Calcium Do You Need?
Use our Calcium Calculator to find out.
Sources of Calcium


Calcium-Rich Food Sources


Food is the best source of calcium. Dairy products, such as low-fat and non-fat milk, yogurt and cheese are high in calcium. Certain green vegetables and other foods contain calcium in smaller amounts. Some juices, breakfast foods, soymilk, cereals, snacks, breads and bottled water have calcium that has been added. If you drink soymilk or another liquid that is fortified with calcium, be sure to shake the container well as calcium can settle to the bottom.
A simple way to add calcium to many foods is to add a single tablespoon of nonfat powdered milk, which contains about 50 mg of calcium. About two-to-four tablespoons can be added to most recipes.
Reading Food Labels - How Much Calcium am I Getting?
To determine how much calcium is in a particular food, check the nutrition facts panel of the food label for the daily value (DV) of calcium. Food labels list calcium as a percentage of the DV. This amount is based on 1,000 mg of calcium per day. For example:
30% DV of calcium equals 300 mg.
20% DV of calcium equals 200 mg of calcium.
15% DV of calcium equals 150 mg of calcium.
Calcium Supplements


The amount of calcium you need from a supplement depends on the amount of calcium you get from food. Aim to get the recommended daily amount of calcium you need from food first and supplement only if needed to make up for any shortfall. If you get enough calcium from the foods you eat, then you don’t need to take a supplement. In fact, there is no added benefit to taking more calcium than you need in supplements and doing so may even have some risks.  
In general, you shouldn’t take supplements that you don’t need. Calcium supplements are available without a prescription in a wide range of preparations (including chewable and liquid) and in different amounts. The best supplement is the one that meets your needs based on convenience, cost and availability. When choosing the best supplement to meet your needs, keep the following in mind:
Choose brand-name supplements with proven reliability. Look for labels that state “purified” or have the USP (United States Pharmacopeia) symbol. The “USP Verified Mark” on the supplement label means that the USP has tested and found the calcium supplement to meet certain standards for purity and quality.
Read the product label carefully to determine the amount of elemental calcium, which is the actual amount of calcium in the supplement, as well as how many doses or pills to take. When reading the label, pay close attention to the “amount per serving” and “serving size.”
Calcium is absorbed best when taken in amounts of 500 – 600 mg or less. This is the case when you eat calcium rich foods or take supplements. Try to get your calcium-rich foods and/or supplements in smaller amounts throughout the day, preferably with a meal. While it's not recommended, taking your calcium all at once is better than not taking it at all.
Take most calcium supplements with food. Eating food produces stomach acid that helps your body absorb most calcium supplements. The one exception to the rule is calcium citrate, which can absorb well when taken with or without food.
When starting a new calcium supplement, start with a smaller amount to better tolerate it. When switching supplements, try starting with 200-300 mg every day for a week, and drink an extra 6-8 ounces of water with it. Then gradually add more calcium each week.
Side effects from calcium supplements, such as gas or constipation may occur. If increasing fluids in your diet does not solve the problem, try another type or brand of calcium. It may require trial and error to find the right supplement for you, but fortunately there are many choices.
Talk with your healthcare provider or pharmacist about possible interactions between prescription or over-the-counter medications and calcium supplements.
What is Vitamin D and What Does it Do?


Vitamin D plays an important role in protecting your bones and your body requires it to absorb calcium. Children need vitamin D to build strong bones, and adults need it to keep their bones strong and healthy. If you don't get enough vitamin D, you may lose bone, have lower bone density, and you're more likely to break bones as you age.
How Much Vitamin D Do You Need?


Women and Men
Under age 50
400-800 international units (IU) daily**
Age 50 and older
800-1,000 IU daily**
**Some people need more vitamin D. According to the Institute of Medicine (IOM), the safe upper limit of vitamin D is 4,000 IU per day for most adults.
Sources of Vitamin D


There are three ways to get vitamin D:
Sunlight
Food
Supplements
Sunlight


Your skin makes vitamin D from the ultra-violet light (UVB rays) in sunlight. Your body is able to store the vitamin and use it later. The amount of vitamin D your skin makes depends on time of day, season, latitude, skin pigmentation and other factors. Depending on where you live, vitamin D production may decrease or be completely absent during the winter.
Because of concerns about skin cancer, many people stay out of the sun, cover up with clothing and use either sunscreen or sunblock to protect their skin. The use of sunscreen or sunblock is probably the most important factor that limits the ability of the skin to make vitamin D. Even an SPF (sun protection factor) of 8 reduces the production of vitamin D by 95 percent. Because of the cancer risk from the sun, most people need to get vitamin D from other sources, including eating foods rich in vitamin D and taking vitamin D supplements.
Food


Vitamin D is naturally available in only a few foods, including fatty fish like wild-caught mackerel, salmon and tuna. Vitamin D is also added to milk and to some brands of other dairy products, orange juice, soymilk and cereals.
Check the food label to see if vitamin D has been added to a particular product. One eight ounce serving of milk usually has 25% of the daily value (DV) of vitamin D. The DV is based on a total daily intake of 400 IU of vitamin D. So, a serving of milk with 25% of the DV of vitamin D contains 100 IU of the vitamin.
It is very difficult to get all the vitamin D you need from food alone. Most people need to take vitamin D supplements to get enough of the nutrient needed for bone health.
Supplements


If you aren't getting enough vitamin D from sunlight and food, consider taking a supplement. But, before adding a vitamin D supplement, check to see if any of the other supplements, multivitamins or medications you  take contain vitamin D. Many calcium supplements also contain vitamin D.
There are two types of vitamin D supplements. They are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Both types are good for bone health.
Vitamin D supplements can be taken with or without food. While your body needs vitamin D to absorb calcium, you do not need to take vitamin D at the same time as a calcium supplement. If you need help choosing a vitamin D supplement, ask your healthcare provider or pharmacist to recommend one.
How Much Vitamin D Should You Supplement?
To figure out how much vitamin D you need from a supplement, subtract the total amount of vitamin D you get each day from the recommended total daily amount for your age. For example, a 55 year old woman who gets 400 IU of vitamin D from her calcium supplement should take between 400 and 600 additional IU of vitamin D to meet the 800 - 1,000 IU recommended for her age.
Vitamin D Deficiency: Are You at Risk?


Vitamin D deficiency occurs when you are not getting the recommended level of vitamin D over time. Certain people are at higher risk for vitamin D deficiency, including:
People who spend little time in the sun or those who regularly cover up when outdoors;
People living in nursing homes or other institutions or who are homebound;
People with certain medical conditions such as Celiac disease and inflammatory bowel disease;
People taking medicines that affect vitamin D levels such as certain anti-seizure medicines;
People with very dark skin;
Obese or very overweight people; and
Older adults with certain risk factors.
Talk to your healthcare provider if you meet any of these risk factors or  think you might be at risk of vitamin D deficiency. If you have osteoporosis and also have a vitamin D deficiency, your healthcare provider may temporarily prescribe a higher dose of vitamin D.

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