Supplement Forms/Alternate Names

  • Bonemeal
  • Calcium Aspartate
  • Calcium Carbonate
  • Calcium Chelate
  • Calcium Citrate
  • Calcium Citrate Malate
  • Calcium Gluconate
  • Calcium Lactate
  • Calcium Orotate
  • Dolomite
  • Oyster Shell Calcium
  • Tricalcium Phosphate

Calcium is the most abundant mineral in the body, making up nearly 2% of total body weight. More than 99% of the calcium in your body is found in your bones, but the other 1% is perhaps just as important for good health. Many enzymes depend on calcium in order to work properly, as do your nerves, heart, and blood-clotting mechanisms.

To build bone, you need to have enough calcium in your diet. But in spite of calcium-fortified orange juice and the best efforts of the dairy industry, most Americans are calcium deficient. 1 Calcium supplements are a simple way to make sure you are getting enough of this important mineral.

One of the most important uses of calcium is to help prevent and treat osteoporosis, the progressive loss of bone mass to which menopausal women are especially vulnerable. Calcium works best when combined with vitamin D.

Other meaningful evidence suggests that calcium may have an additional important use: reducing PMS symptoms.



Here are the recommendations from the Institute of Medicine: 198

  • 0-6 months: 200 mg
  • 7-12 months: 260 mg
  • 1-3 years: 700 mg
  • 4-8 years: 1,000 mg
  • 9-18 years: 1,300 mg
  • 19-50 years: 1,000 mg
  • 51-70 years
    • Males: 1,000 mg
    • Females: 1,200 mg
  • 71 and older: 1,200 mg

The recommendations for women who are pregnant or nursing are:

  • Under 19 years: 1,300 mg
  • 19 years and older: 1,000 mg

Food Sources

The National Institutes of Health's Office of Dietary Supplements offers this list of foods that are high in calcium: 201

Food Serving size Calcium content (milligrams [mg]) % Daily Value
Yogurt, plain, low-fat 8 ounces 415 42
Orange juice, calcium-fortified 6 ounces 375 38
Yogurt, fruit, low-fat 8 ounces 338-384 34-38
Mozzarella, part-skim 1.5 ounces 333 33
Sardines, canned in oil, with bones 3 ounces 325 33
Cheddar cheese 1.5 ounces 307 31
Milk, non-fat 8 ounces 299 30
Milk, reduced-fat 8 ounces 293 29
Milk, buttermilk 8 ounces 282-350 28-35
Milk, whole 8 ounces 276 28
Tofu, firm (with calcium sulfate) ½ cup 253 25
Pink salmon with bones, canned 3 ounces 181 18
Cottage cheese, 1% milk fat 1 cup 138 14
Tofu, soft (with calcium sulfate) ½ cup 138 14
Instant breakfast drink 8 ounces 105-250 10-25
Frozen yogurt, vanilla ½ cup 103 10
Ready-to-eat cereal, calcium-fortified 1 cup 100-1,000 10-100
Turnip greens, fresh, boiled ½ cup 99 10
Kale, fresh, cooked 1 cup 94 9
Kale, raw, chopped 1 cup 90 9

In addition to food sources, many forms of calcium supplements are available on the market, each with its own advantages and disadvantages.

Calcium Absorption

To absorb calcium, your body also needs an adequate level of vitamin D (for more information, see the article on Vitamin D ).

Various medications may impair calcium absorption or metabolism, either directly or through effects on vitamin D. People who use these may benefit by taking extra calcium and vitamin D. Implicated medications include corticosteroids , 30-32heparin , 33-35isoniazid , 36-38 and anticonvulsants . 39-45Note: Calcium carbonate might interfere with the effects of anticonvulsant drugs, and for that reason should not be taken at the same time of day. 46,47

Naturally Derived Forms of Calcium

These forms of calcium come from bone, shells, or the earth: bonemeal, oyster shell, and dolomite. Animals concentrate calcium in their shells, and calcium is found in minerals in the earth. These forms of calcium are economical, and you can get as much as 500 mg to 600 mg in one tablet. However, there are concerns that the natural forms of calcium supplements may contain significant amounts of lead. 2 The level of contamination has decreased in recent years, but still may present a health risk. 3,4 Calcium supplements rarely list the lead content of their source, although they should. The lead concentration should always be less than 2 parts per million.

Refined Calcium Carbonate

This is the most common commercial calcium supplement, and it is also used as a common antacid. Calcium carbonate is one of the least expensive forms of calcium, but it can cause constipation and bloating, and it may not be well absorbed by people with reduced levels of stomach acid. Taking it with meals improves absorption because stomach acid is released to digest the food. 121 (See the section, Chelated Calcium, below.)

Chelated Calcium

Chelated calcium is calcium bound to an organic acid (citrate, citrate malate, lactate, gluconate, aspartate, or orotate). The chelated forms of calcium offer some significant advantages and disadvantages compared with calcium carbonate.

Certain forms of chelated calcium (calcium citrate and calcium citrate malate) are widely thought to be significantly better absorbed and more effective for osteoporosis treatment than calcium carbonate. However, while some studies support this belief, 6,7,9,10 others do not. 8,122,123 The discrepancy may be due to the particular calcium carbonate products used; some calcium carbonate formulations may dissolve better than others.

One study found that calcium citrate malate in orange juice is markedly better absorbed than tricalcium phosphate/calcium lactate in orange juice. 148

A form of calcium called active absorbable algal calcium (AAACa) has also been promoted as superior to calcium carbonate, but the study upon which claims of benefit are founded actually used quite questionable statistical methods (technically, post-hoc subgroup analysis). 133

Chelated calcium is much more expensive and bulkier than calcium carbonate. In other words, you have to take larger pills, and more of them, to get enough calcium. It is not at all uncommon to need to take five or six large capsules daily to supply the necessary amount, a quantity some people may find troublesome.

Therapeutic Dosages

Unlike some supplements, calcium is not taken at extra high doses for special therapeutic benefit. Rather, for all its uses, it should be taken in the amounts listed under Requirements/Sources, along with the recommended level of vitamin D. (See the article on vitamin D for proper dosage amounts.)

Calcium absorption studies have found evidence that your body cannot absorb more than 500 mg of calcium at one time. 11 Therefore, it is most efficient to take your total daily calcium in two or more doses.

Use of prebiotics known as "inulin fructans" may improve calcium absorption. 149

It is not possible to put all the calcium you need in a single multivitamin/mineral tablet, so this is one supplement that should be taken on its own. Furthermore, if taken at the same time, calcium may interfere with the absorption of chromium and manganese . 12,13,14 This means that it is best to take your multivitamin and mineral pill at a separate time from your calcium supplement.

Although the calcium present in some antacids or supplements may alter the absorption of magnesium , this effect apparently has no significant influence on overall magnesium status. 15,16 Calcium may also interfere with iron absorption, 17-22,150 but the effect may be too slight to cause a problem. Some studies show that calcium may decrease zinc absorption when the two are taken together as supplements; however, studies have found that, in the presence of meals, zinc levels may be unaffected by increases of either dietary or supplemental calcium. 23-29

Therapeutic Uses

According to most, though not all studies, use of calcium (especially in the form of calcium citrate) combined with vitamin D may modestly slow the bone loss that leads to osteoporosis . 48-55,151-153 Calcium and vitamin D may help prevent falls that lead to osteoporotic fractures. In a review of 26 randomized trials, researchers found that the two supplements lowered the risk of falls in high-risk elderly people. 200

A rather surprising potential use of calcium came to light when a large, well-designed study found that calcium is an effective treatment for premenstrual syndrome (PMS). 56 Calcium supplementation reduced all major symptoms, including headache, food cravings, moodiness, and fluid retention. It is at least remotely possible that there may be a connection between these two uses of calcium: weak evidence hints that PMS might be an early sign of future osteoporosis. 57,58

One small but carefully conducted study suggests that getting enough calcium may help control symptoms of menstrual pain . 89

Some, but not all, observational and intervention studies have found evidence that calcium supplementation may reduce the risk of colon cancer . 59,134-135,154-156 Risk reduction might continue for years after calcium supplements are stopped. 182 However, calcium supplements might increase risk of prostate cancer in men, as discussed in the Safety Issues section. For menopausal women, calcium supplementation, especially with vitamin D added, may reduce cancer risk in general. 187

Individuals who are deficient in calcium may be at greater risk of developing high blood pressure . 60,61,126 Among individuals who already have hypertension, increased intake of calcium might slightly decrease blood pressure, according to some, but not all, studies. 62,127 Weak evidence hints that use of calcium by pregnant mothers might reduce risk of hypertension in their children. 185

Calcium supplements might slightly improve the cholesterol profile. 63,64,124

Calcium supplementation has also been tried as a treatment to prevent preeclampsia in pregnant women. While the evidence from studies is conflicting, 66-68,157-15 calcium supplementation might offer at least a minimal benefit.

The drug metformin , used for diabetes, interferes with the absorption of vitamin B 12 . Interestingly, calcium supplements may reverse this, allowing the B 12 to be absorbed normally. 70

Rapid weight loss in overweight postmenopausal women appears to slightly accelerate bone loss. 71,136 For this reason, it may make sense to take calcium and vitamin D supplements when deliberately losing weight. It has been additionally suggested that calcium supplements, or high-calcium diets, may directly enhance weight loss, but current evidence is more negative than positive. 72,130,137,159-165,186,188,189,191

Finally, calcium is also sometimes recommended for attention deficit disorder , migraine headaches , and periodontal disease , but there is as yet no meaningful evidence that it is effective for these conditions.

It is important to note that despite the benefits of calcium supplementation for certain conditions, a large, placebo-controlled trial involving over 36,000 post-menopausal women found that daily supplements of 1,000 mg of calcium carbonate combined with 400 IU of vitamin D3 for an average of 7 years did not significantly reduce death rates from all causes. 196

What Is the Scientific Evidence for Calcium?


A number of double-blind, placebo-controlled studies indicate that calcium supplements (especially as calcium citrate, and taken with vitamin D) are slightly helpful in preventing and slowing down bone loss in postmenopausal women. 73-76,138,165-169,180 Contrary to some reports, milk does appear to be a useful source of calcium for this purpose. 183-184

However, the effect of calcium supplementation in any form is relatively mild and may not be strong enough to reduce the rate of osteoporotic fractures. Note that the use of calcium and vitamin D must be continual. Any improvements in bone density rapidly disappear once the supplements are stopped. 77 A large randomized trail of over 3,000 postmenopausal women aged 65-71 years old found that 3 years of daily supplementation with calcium and vitamin D was not associated with a significant reduction in the incidence of fractures. 197

In a much larger observational study (not a randomized trial) involving 61,433 women aged 39-73, researchers investigated the effects of dietary calcium (as opposed to supplements) on the risk of osteoporosis and fracture over a 19-year period. 199 They found that women who consumed less than 750 mg/day of calcium had a higher rate of osteoporotic fractures in any location. Unexpectedly, however, the study also found that those who consumed the highest amounts of calcium (over 1,137 mg/day) did not have a comparatively reduced rate of fractures or osteoporosis. Indeed, this high dietary intake was associated with an increase in the number of hip fractures for reasons the authors could not completely explain.

Other studies have found that calcium carbonate may not be effective. 170-171

One study found benefits for male seniors using a calcium and vitamin D-fortified milk product. 172 (See, however, possible increased risk of prostate cancer discussed in Safety Issues .)

Calcium and vitamin D supplementation may help bones heal that have become fractured due to bone thinning. 139

Calcium supplements may do a better job of strengthening bones when people have relatively high protein intake. 125

Heavy exercise causes increased calcium loss through sweat, and the the body does not compensate for this by reducing calcium loss in the urine. 190 The result can be a net calcium loss great enough so that it presents health concerns for menopausal women, already at risk for osteoporosis. One study found that use of an inexpensive calcium supplement (calcium carbonate), taken at a dose of 400 mg twice daily, is sufficient to offset this loss. 190

Calcium supplementation could, in theory, be useful for young girls as a way to "put calcium in the bank"—building up a supply for the future in order to prevent later osteoporosis. However, surprisingly, the benefits seen in studies have been modest to nonexistent, and this approach may only produce results when exercise is also increased. 79-81,140-143,173-175,181

One study found that in calcium-deficient pregnant women, calcium supplements can improve the bones of their unborn children. 82

Evidence suggests that the use of calcium combined with vitamin D can help protect against the bone loss caused by corticosteroid drugs, such as prednisone. A review of five studies covering a total of 274 participants reported that calcium and vitamin D supplementation significantly prevented bone loss in corticosteroid-treated individuals. 83 For example, in a 2-year, double-blind, placebo-controlled study that followed 65 individuals with rheumatoid arthritis taking low-dose corticosteroids, daily supplementation with 1,000 mg of calcium and 500 IU of vitamin D reversed steroid-induced bone loss, causing a net bone gain. 84

There is some evidence that essential fatty acids may enhance the effectiveness of calcium. In one study, 65 postmenopausal women were given calcium along with either placebo or a combination of omega-6 fatty acids (from evening primrose oil ) and omega-3 fatty acids (from fish oil ) for a period of 18 months. At the end of the study period, the group receiving essential fatty acids had higher bone density and fewer fractures than the placebo group. 85 However, a 12-month, double-blind trial of 42 postmenopausal women found no benefit. 86 The explanation for the discrepancy may lie in the differences between the women studied. The first study involved women living in nursing homes, while the second studied healthier women living on their own. The latter group of women may have been better nourished and already received enough essential fatty acids in their diet.

Premenstrual Syndrome (PMS)

According to a large and well-designed study published in a 1998 issue of American Journal of Obstetrics and Gynecology, calcium supplements are a simple and effective treatment for a wide variety of PMS symptoms. 87 In a double-blind, placebo-controlled study of 497 women, 1,200 mg daily of calcium as calcium carbonate reduced PMS symptoms by half over a period of three menstrual cycles. These symptoms included mood swings, headaches, food cravings, and bloating. These results corroborate earlier, smaller studies. 88,89

High Cholesterol

In a 12-month study of 223 postmenopausal women, use of calcium citrate at a dose of 1 g daily improved the ratio of HDL (“good”) cholesterol levels to LDL (“bad”) cholesterol levels. 124 The extent of this improvement was statistically significant (as compared to the placebo group), but not very large in practical terms. Similarly modest benefits were seen in a previous, smaller double-blind, placebo-controlled study. 63 A third double-blind, placebo-controlled study failed to find any statistically significant effects. 64

Colon Cancer

Evidence from observational studies showed that a high calcium intake is associated with a reduced incidence of colon cancer , 91 but not all studies have found this association. 92

Some but not all evidence from intervention trials supports these findings. 90,176-178

A 4-year, double-blind, placebo-controlled study followed 832 individuals with a history of colon polyps. 90 Participants received either 3 g daily of calcium carbonate or placebo. The calcium group experienced 24% fewer polyps overall than the placebo group. Since colon polyps are the precursor of most colon cancer, this finding strongly suggests benefit. Combing the results for two trials, involving a total of 1,346 subjects also with a history of polyps, researchers found that 1,200 mg or 2,000 mg of daily elemental calcium led to a significant reduction in polyp recurrence compared to placebo over a 3-4 year period. 193 Another, large-sized study found that calcium carbonate at a dose of 1,200 mg daily may have a more pronounced effect on dangerous polyps than on benign ones. 144

However, a gigantic (36,282 participant), very long-term (average 7 years) study of postmenopausal women failed to find that calcium carbonate supplements at a dose of 1,000 mg daily had any effect on the incidence of colon cancer. 178 Given these conflicting results, if calcium supplementation does have an effect on colon cancer risk, it is probably small.


A very large randomized, placebo-controlled trial of over 36,000 postmenopausal women found daily supplementation with 1,000 mg of calcium plus 400 IU of vitamin D did not reduce or prevent hypertension during 7 years of follow-up. These results are possibly limited by non-study calcium use. 195

Safety Issues

In general, it is safe to take up to 2,500 mg of calcium daily (1,000 mg/day in infants 12 months old or younger), although this is more than you need. 93,119,198 Greatly excessive intake of calcium can cause numerous side effects, including dangerous or painful deposits of calcium within the body.

Note: If you have cancer, hyperparathyroidism, or sarcoidosis, you should take calcium only under a physician's supervision.

Some evidence hints that use of calcium supplements might slightly increase kidney stone risk. 96,132,178 However, increased intake of calcium from food does not seem to have this effect and could even help prevent stones. 94,95,97,132 One study found that if calcium supplements are taken with food, there is no increased risk. 146 Calcium citrate supplements may be particularly safe regarding kidney stones because the citrate portion of this supplement is used to treat kidney stones. 147

There is preliminary evidence that calcium supplementation in healthy, post-menopausal women may slightly increase the risk of cardiovascular events, such as myocardial infarction. However, it remains far from clear whether this possible risk outweighs the benefits of calcium supplementation in this population. 192,194

Large observational studies have found that, in men, higher intakes of calcium are associated with an increased risk of prostate cancer. 98,99,100,179 This seems to be the case whether the calcium comes from milk or from calcium supplements.

Calcium supplements combined with high doses of vitamin D might interfere with some of the effects of drugs in the calcium channel blocker family. 101 It is very important that you consult your physician before trying this combination.

Concerns have been raised that the aluminum in some antacids may not be good for you. 102 There is some evidence that calcium citrate supplements might increase the absorption of aluminum; 103-107 for this reason, it might not be a good idea to take calcium citrate at the same time of day as aluminum-containing antacids. Another option is to use different forms of calcium, or to avoid antacids containing aluminum.

When taken over the long term, thiazide diuretics tend to increase levels of calcium in the body by decreasing the amount excreted by the body. 108-111 It is not likely that this will cause a problem. Nonetheless, if you are using thiazide diuretics, you should consult with your physician on the proper doses of calcium and vitamin D for you.

Finally, calcium may interfere with the absorption of antibiotics in the tetracycline and fluoroquinolone families as well as thyroid hormone. 112-118 If you are taking any of these drugs, you should take your calcium supplements at least 2 hours before or after your medication dose.

Interactions You Should Know About

  • You may need more calcium if you are taking:
  • If you are taking aluminum hydroxide , you should take calcium citrate at least 2 hours apart to avoid increasing aluminum absorption.
  • You may need more calcium if you are taking the following anticonvulsants:
  • If you are taking the following medications, you should take your calcium supplement at least 2 hours before or after your dose of medication because calcium interferes with the absorption (and vice versa):
  • Do not take extra calcium except on the advice of a physician if you are taking Thiazide diuretics .
  • Do not take calcium together with high-dose vitamin D except on the advice of a physician if you are taking calcium channel blockers .
  • You may need extra calcium if you are taking:
    • Iron
    • Manganese
    • Zinc
    • Chromium
    • Ideally, you should take calcium at a different time of day from these other minerals because it may interfere with their absorption.
  • It may be advisable to wait 2 hours after taking calcium supplements to eat soy (or vice versa). A constituent of soy called phytic acid can interfere with the absorption of calcium.
  • Taking supplemental calcium may be helpful if you are taking metformin .

Revision Information