What is calcium as a dietary supplement?

Overview

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

To build bone, a person needs to have enough calcium in his or her diet. However, even with the availability of calcium-fortified orange juice and with the best efforts of the dairy industry, most Americans are calcium deficient. Calcium supplements are a simple way to make sure one is 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 use: reducing symptoms of premenstrual syndrome (PMS).

Requirements and Sources

Although there are some variations between recommendations issued by different groups, the official U.S. and Canadian recommendations for daily intake of calcium (in milligrams) are as follows: infants to six months of age (210) and seven to twelve months of age (270); children one to three years of age (500) and four to eight years of age (800); children nine to eighteen years of age (1,300); adults age nineteen to fifty years (1,000), age fifty-one years and older (1,200); and pregnant and nursing girls (1,300) and women (1,000).

To absorb calcium, the body also needs an adequate level of vitamin D. Various
medications may impair calcium absorption or metabolism, either directly or
through effects on vitamin D. Implicated medications include corticosteroids, heparin, isoniazid, and anticonvulsants.
People who use these medications may benefit by taking extra calcium and vitamin
D. Calcium carbonate might interfere with the effects of anticonvulsant drugs, so
it should not be taken at the same time of day.

Milk, cheese, and other dairy products are excellent sources of calcium. Other good sources include orange juice or soy milk fortified with calcium, fish (such as sardines) canned with its bones, dark green vegetables, nuts and seeds, and calcium-processed tofu. Many forms of calcium supplements are available on the market, each with its own advantages and disadvantages.

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

Refined calcium carbonate. Refined calcium carbonate 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.

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, others do not. The discrepancy may come from 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.

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

Chelated calcium is much more expensive and bulkier than calcium carbonate. In other words, a person would have to take larger pills, and more of them, to get enough calcium. It is not 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 recommended amounts, along with the recommended level of vitamin D.

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

It is not possible to put all the calcium one needs in a single multivitamin-multimineral 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. This means that it is best to take the multivitamin-multimineral pill at a different time than the calcium supplement.

Although the calcium in some antacids or supplements may alter the absorption of magnesium, this effect apparently has no significant influence on overall magnesium status. Calcium may also interfere with iron absorption, 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. Finally, the use of prebiotics known as inulin fructans may improve calcium absorption.

Therapeutic Uses

According to most studies, the use of calcium (especially in the form of calcium citrate) with vitamin D may modestly slow the bone loss that leads to osteoporosis. A rather surprising potential use of calcium came to light when a large, well-designed study found that calcium is an effective treatment for PMS. Calcium supplementation reduced all major symptoms, including headache, food cravings, moodiness, and fluid retention. It is 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. One small but carefully conducted study suggests that getting enough calcium may help control symptoms of menstrual pain too.

Some observational and intervention studies have found evidence that calcium supplementation may reduce the risk of colon cancer. Risk reduction might continue for years after calcium supplements are stopped. However, calcium supplements might increase risk of prostate cancer in men. For menopausal women, the use of calcium supplements, especially with vitamin D added, may reduce cancer risk in general.

Persons who are deficient in calcium may be at greater risk of developing high
blood pressure. Among persons who already have hypertension,
increased intake of calcium might slightly decrease blood
pressure, according to some studies. Weak evidence hints that
the use of calcium by pregnant women might reduce the risk of hypertension in
their children. Calcium supplementation has also been tried as a treatment to
prevent preeclampsia in pregnant women. While the evidence from studies is
conflicting, calcium supplementation might offer at least a minimal benefit.

The drug metformin, used for diabetes, interferes with the absorption of vitamin B12. Calcium supplements may reverse this, allowing the B12 to be absorbed normally. Also, calcium supplements might slightly improve the cholesterol profile.

Rapid weight loss in overweight postmenopausal women appears to slightly accelerate bone loss. 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 the evidence is more negative than positive.

Finally, calcium is also sometimes recommended for attention deficit
disorder, migraine headaches, and periodontal
disease, but there is 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
more than 36,000 postmenopausal women found that daily supplements of 1,000 mg of
calcium carbonate combined with 400 international units (IU) of vitamin D(3) for
an average of seven years did not significantly reduce death rates from all
causes.

Scientific Evidence

Osteoporosis. 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 bone loss in postmenopausal women. Contrary to some reports, milk does appear to be a useful source of calcium for this purpose. 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. The use of calcium and vitamin D must be continual. Any improvements in bone density rapidly disappear once the supplements are stopped. A large study of more than three thousand postmenopausal women age sixty-five to seventy-one years found that three years of daily supplementation with calcium and vitamin D was not associated with a significant reduction in the incidence of fractures. Calcium carbonate may not be effective.

One study found benefits for elderly men using a calcium- and vitamin D-fortified milk product. Calcium and vitamin D supplementation may help bones heal that have become fractured because of bone thinning. Also, calcium supplements may do a better job of strengthening bones when people have relatively high protein intake.

Heavy exercise leads to a loss of calcium through sweat, and the body does not compensate for this by reducing calcium loss in the urine. 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 the use of an inexpensive calcium supplement (calcium carbonate), taken at a dose of 400 mg twice daily, is sufficient to offset this loss.

Calcium supplementation could, in theory, be useful for young girls as a way to build a supply of calcium for the future to prevent later osteoporosis. However, the benefits seen in studies have been modest to nonexistent, and this approach may only produce results when exercise is also increased.

Evidence suggests that the use of calcium with vitamin D can help protect against the bone loss caused by corticosteroid drugs, such as prednisone. A review of five studies covering 274 participants reported that calcium and vitamin D supplementation significantly prevented bone loss in corticosteroid-treated persons. For example, in a two-year, double-blind, placebo-controlled study that followed sixty-five persons 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. Also, one study found that in calcium-deficient pregnant women, calcium supplements can improve the bones of their unborn children.

There is some evidence that essential fatty acids may enhance the effectiveness of calcium. In one study, sixty-five postmenopausal women were given calcium with either placebo or a combination of omega-6 fatty acids (from evening primrose oil) and omega-3 fatty acids (from fish oil) for eighteen 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. However, a twelve-month, double-blind trial of forty-two postmenopausal women found no benefit. 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 may have been receiving enough essential fatty acids in their diet.

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

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

Colon cancer. Evidence from observational studies showed that a high calcium intake is associated with a reduced incidence of colon cancer, but not all studies have found this association. Some evidence from intervention trials supports these findings.

A four-year, double-blind, placebo-controlled study followed 832 persons with a history of colon polyps. Participants received either 3 g daily of calcium carbonate or placebo. The calcium group experienced 24 percent fewer polyps overall than the placebo group. Because colon polyps are the precursor of most colon cancer, this finding strongly suggests benefit. Combining the results for two trials, involving a total of 1,346 participants also with a history of polyps, researchers found that 1,200 or 2,000 mg of daily elemental calcium led to a significant reduction in polyp recurrence compared with placebo in a three-to-four-year period. Another large 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.

A gigantic (36,282-participant) and long-term (average of seven 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. Given these conflicting results, if calcium supplementation does have an effect on colon cancer risk, it is probably small.

Hypertension. A large randomized, placebo-controlled trial of more than 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 seven years of follow-up. These results are possibly limited by calcium use unrelated to the study.

Safety Issues

In general, it is safe to take up to 2,500 mg of calcium daily, although this
is more than a person needs. Excessive intake of calcium can cause numerous side
effects, including dangerous or painful deposits of calcium within the body. For
persons with cancer, hyperparathyroidism, or sarcoidosis,
calcium should be taken only under a physician’s supervision.

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

There is preliminary evidence that calcium supplementation in healthy, postmenopausal 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.

Large observational studies have found that, in men, higher intakes of calcium
are associated with an increased risk of prostate
cancer. 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. It is
very important that one consult a physician before trying this combination.

Concerns have been raised that the aluminum in some antacids may be harmful. There is some evidence that calcium citrate supplements might increase the absorption of aluminum; for this reason, one probably should not take calcium citrate at the same time of day as aluminum-containing antacids. Other options are 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. It is
not likely that this will cause a problem. Nonetheless, persons using thiazide
diuretics should consult with a physician on the proper doses of calcium and
vitamin D.

Finally, calcium may interfere with the absorption of antibiotics in the
tetracycline and fluoroquinolone families and with
thyroid hormone. Persons taking any of these drugs should take calcium supplements
a minimum of two hours before or after the medication dose.

Important Interactions

Persons may need more calcium if also taking corticosteroids, heparin, or isoniazid. Persons taking aluminum hydroxide should take it and calcium citrate a minimum of two hours apart to avoid increasing aluminum absorption.

Persons may need more calcium if they are also taking any of the following anticonvulsants: phenytoin (Dilantin), carbamazepine, phenobarbital, or primidone. It may be advisable to take the dose of anticonvulsant and the calcium supplement a minimum of two hours apart because each substance interferes with the other’s absorption.

For persons taking antibiotics in the tetracycline or fluoroquinolone (cipro, floxin, noroxin) families or taking thyroid hormone, the calcium supplement should be taken a minimum of two hours before or after the dose of medication, because calcium interferes with absorption (and vice versa). Also, one should not take extra calcium except on the advice of a physician if also taking thiazide diuretics. Finally, one should not take calcium with high-dose vitamin D except on the advice of a physician if also taking calcium channel blockers.

Persons may need extra calcium if also taking iron, manganese, zinc, or chromium. Ideally, one should take calcium at a different time of day from these other minerals because it may interfere with their absorption.

Finally, it may be advisable to wait two 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.

Bibliography

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