Calcium deficiency has been implicated as a possible cause of GH.^1,2 In two preliminary studies, women who developed GH were found to have significantly lower dietary calcium intake than did pregnant women with normal blood pressure.^3,4 Calcium supplementation has significantly reduced the incidence of GH in preliminary studies⁵ and in many,^{5,7,8,9,10,11} though not all,¹² double-blind trials. Calcium supplements may be most effective in preventing GH in women who have low dietary intake of calcium. The National Institutes of Health (NIH) recommends an intake of 1,200 to 1,500 mg of calcium daily during normal pregnancy.¹³ In women at risk of GH, studies showing reduced incidence have typically used 2,000 mg of supplemental calcium per day,^{14,15,5,7,9,11} without any reported maternal or fetal side effects.^14,15 Nonetheless, many doctors continue to suggest amounts no higher than 1,500 mg per day.

Calcium deficiency has been associated with preeclampsia.¹⁵ In numerous controlled trials, oral calcium supplementation has been studied as a possible preventive measure.^16 17 1819 While most trials have found a significant reduction in the incidence of preeclampsia with calcium supplementation,^161722231925 One study reported that calcium supplementation reduced both the severity of preeclampsia and the mortality rate in the infants.¹⁸

An analysis of double-blind trials46 found calcium supplementation to be highly effective in preventing preeclampsia. However, a large and well-designed double-blind trial and a critical analysis of six double-blind trials concluded that calcium supplementation did not reduce the risk of preeclampsia in healthy women at low risk for preeclampsia.²⁷ For healthy, high-risk (in other words, calcium deficient) women, however, the data show a clear and statistically significant beneficial effect of calcium supplementation in reducing the risk of preeclampsia.^{2723183118333435191938 39 4041}

The National Institutes of Health recommends an intake of 1,200 to 1,500 mg of elemental calcium daily during normal pregnancy.⁴² In women at risk of preeclampsia, most trials showing reduced incidence have used 2,000 mg of supplemental calcium per day.¹⁷ Nonetheless, many doctors continue to suggest amounts no higher than 1,500 mg per day.

Calcium needs double during pregnancy.³³ Low dietary intake of this mineral is associated with increased risk of preeclampsia, a potentially dangerous (but preventable) condition characterized by high blood pressure and swelling. Supplementation with calcium may reduce the risk of pre-term delivery, which is often associated with preeclampsia. Calcium may reduce the risk of pregnancy-induced hypertension,³⁴ though these effects are more likely to occur in women who are calcium deficient.^35,36 Supplementation with up to 2 grams of calcium per day by pregnant women with low dietary calcium intake has been shown to improve the bone strength of the fetuses.³⁷

Pregnant women should consume 1,500 mg of calcium per day from all sources—food plus supplements. Food sources of calcium include dairy products, dark green leafy vegetables, tofu, sardines (canned with edible bones), salmon (canned with edible bones), peas, and beans.

A woman should continue to take prenatal vitamins in order to meet the nutrient requirements of breast-feeding. Especially important is continued intake of calcium and calcium-rich foods.

Women who consume more calcium from their diets are less likely to suffer severe PMS.³⁸ A large double-blind trial found that women who took 1,200 mg per day of calcium for three menstrual cycles had a 48% reduction in PMS symptoms, compared to a 30% reduction in the placebo group.³⁹ Other double-blind trials have shown that supplementing 1,000 mg of calcium per day relieves premenstrual symptoms.^40,41

Calcium needs double during pregnancy.⁴² Low dietary intake of this mineral is associated with increased risk of preeclampsia, a potentially dangerous (but preventable) condition characterized by high blood pressure and swelling. Supplementation with calcium may reduce the risk of pre-term delivery, which is often associated with preeclampsia. Calcium may reduce the risk of pregnancy-induced hypertension,⁴³ though these effects are more likely to occur in women who are calcium deficient.^44,45 Supplementation with up to 2 grams of calcium per day by pregnant women with low dietary calcium intake has been shown to improve the bone strength of the fetuses.⁴⁶

Pregnant women should consume 1,500 mg of calcium per day from all sources—food plus supplements. Food sources of calcium include dairy products, dark green leafy vegetables, tofu, sardines (canned with edible bones), salmon (canned with edible bones), peas, and beans.

In theory, calcium may help prevent menstrual cramps by maintaining normal muscle tone. Muscles that are calcium-deficient tend to be hyperactive and therefore might be more likely to cramp. Calcium supplementation was reported to reduce pain during menses in one double-blind trial,⁴⁷ though another such study found that it relieved only premenstrual cramping, not pain during menses.⁴⁸ Some doctors recommend calcium supplementation for dysmenorrhea, suggesting 1,000 mg per day throughout the month and 250–500 mg every four hours for pain relief, during acute cramping (up to a maximum of 2,000 mg per day).

A preliminary trial showed that bone loss occurred over a one-year period in amenorrheic exercising women despite daily supplementation with 1,200 mg of calcium and 400 IU of vitamin D.⁴⁹ In a controlled study of amenorrheic nursing women, who ordinarily experience brief bone loss that reverses when menstruation returns, bone loss was not prevented by a multivitamin supplement providing 400 IU of vitamin D along with 500 mg twice daily of calcium or placebo.⁵⁰ Despite the lack of evidence that calcium and vitamin D supplements alone are helpful to amenorrheic women, they are still generally recommended to prevent the added burden of calcium and vitamin D deficiency from further contributing to bone loss.⁵¹ Amounts typically recommended are 1,200 to 1,500 mg calcium and 400 to 800 IU vitamin D daily.

Caution: Calcium supplements should be avoided by prostate cancer patients.

Researchers have yet to clearly determine whether lactose-intolerant people absorb less calcium.⁵² As lactose-containing foods are among the best dietary sources of calcium, alternative sources of calcium (from beverages, foods, or supplements) are important for lactose-intolerant people. A typical amount of supplemental calcium is 1,000 mg per day.

Caution: Calcium supplements should be avoided by prostate cancer patients.

The malabsorption that occurs in celiac disease can lead to multiple nutritional deficiencies. The most common nutritional problems in people with celiac disease include deficiencies of essential fatty acids, iron, vitamin D, vitamin K, calcium, magnesium, and folic acid.⁵³Zinc malabsorption also occurs frequently in celiac disease⁵⁴ and may result in zinc deficiency, even in people who are otherwise in remission.⁵⁵ People with newly diagnosed celiac disease should be assessed for nutritional deficiencies by a doctor. Celiac patients who have not yet completely recovered should supplement with a high-potency multivitamin-mineral. Some patients may require even higher amounts of some of these vitamins and minerals—an issue that should be discussed with their healthcare practitioner. Evidence of a nutrient deficiency in a celiac patient is a clear indication for supplementation with that nutrient.

After commencement of a gluten-free diet, overall nutritional status gradually improves. However, deficiencies of some nutrients may persist, even in people who are strictly avoiding gluten. For example, magnesium deficiency was found in 8 of 23 adults with celiac disease who had been following a gluten-free diet and were symptom-free. When these adults were supplemented with magnesium for two years, their bone mineral density increased significantly.⁵⁶

Women who consume more calcium from their diets are less likely to suffer severe PMS.⁵⁷ A large double-blind trial found that women who took 1,200 mg per day of calcium for three menstrual cycles had a 48% reduction in PMS symptoms, compared to a 30% reduction in the placebo group.⁵⁸ Other double-blind trials have shown that supplementing 1,000 mg of calcium per day relieves premenstrual symptoms.^59,60

In theory, calcium may help prevent menstrual cramps by maintaining normal muscle tone. Muscles that are calcium-deficient tend to be hyperactive and therefore might be more likely to cramp. Calcium supplementation was reported to reduce pain during menses in one double-blind trial,⁶¹ though another such study found that it relieved only premenstrual cramping, not pain during menses.⁶² Some doctors recommend calcium supplementation for dysmenorrhea, suggesting 1,000 mg per day throughout the month and 250–500 mg every four hours for pain relief, during acute cramping (up to a maximum of 2,000 mg per day).

A preliminary trial showed that bone loss occurred over a one-year period in amenorrheic exercising women despite daily supplementation with 1,200 mg of calcium and 400 IU of vitamin D.⁶³ In a controlled study of amenorrheic nursing women, who ordinarily experience brief bone loss that reverses when menstruation returns, bone loss was not prevented by a multivitamin supplement providing 400 IU of vitamin D along with 500 mg twice daily of calcium or placebo.⁶⁴ Despite the lack of evidence that calcium and vitamin D supplements alone are helpful to amenorrheic women, they are still generally recommended to prevent the added burden of calcium and vitamin D deficiency from further contributing to bone loss.⁶⁵ Amounts typically recommended are 1,200 to 1,500 mg calcium and 400 to 800 IU vitamin D daily.

Calcium can inhibit cholesterol absorption and synthesis, and some research shows calcium supplements can lower high cholesterol levels.^66,67 A meta-analysis of results from 22 randomized controlled trials with a total of 4,071 participants found calcium supplementation, with or without vitamin D, decreased LDL-cholesterol and increased HDL-cholesterol levels, though the effects were small.⁶⁸ In a placebo-controlled trial in 36,282 women aged 50 years and older, taking 1,000 mg calcium plus 400 IU vitamin D daily led to a small reduction in LDL-cholesterol levels compared with placebo after six years of monitoring.⁶⁹ However, a two-year placebo-controlled trial in 190 premenopausal and 182 postmenopausal women with high cholesterol levels found long-term supplementation with 800 mg calcium daily increased cholesterol levels and resulted in detrimental changes in carotid artery structure, suggesting increased atherosclerosis in postmenopausal participants, but had no impact on these parameters in premenopausal participants.⁷⁰

Although many studies have examined the relationship between calcium supplementation and cardiovascular outcomes, this topic remains controversial. One recent review of trials and meta-analyses concluded modest calcium supplementation may have a small protective effect against heart attack, stroke, and cardiovascular death, especially in women.⁷¹ However, a meta-analysis of 13 randomized controlled trials with more than 42,000 participants found 1,000 mg per day of supplemental calcium, as well as high dietary calcium intake, can substantially increase cardiovascular risk in healthy postmenopausal women.⁷² Yet another large analysis found no cardiovascular benefits or harms from calcium supplementation.⁷³

Some research suggests vitamin D may increase the beneficial effects of calcium. In a randomized controlled trial in 45 women with obesity, those who received 1,200 mg calcium per day plus 50,000 IU vitamin D per week had greater reduction in cholesterol levels than those who received calcium alone or no supplements after three months.⁷⁴

Caution: Calcium supplements should be avoided by prostate cancer patients.

In a preliminary trial, supplementation with 800 mg of calcium per day for one year resulted in a statistically significant 35% reduction in the average TG level among people with elevated cholesterol and triglycerides.⁷⁵ However, in another trial, calcium supplementation had no effect on TG levels.⁷⁶ One of the differences between these two trials was that more people in the former trial had initially elevated TG levels.

Caution: Calcium supplements should be avoided by prostate cancer patients.

Although insufficient when used as the only intervention, calcium supplements help prevent osteoporosis.⁸⁵ Though some of the research remains controversial, the protective effect of calcium on bone mass is one of very few health claims permitted on supplement labels by the U.S. Food and Drug Administration.

In some studies, higher calcium intake has not correlated with a reduced risk of osteoporosis—for example, in women shortly after becoming menopausal⁸⁶ or in men.⁸⁷ However, after about three years of menopause, calcium supplementation does appear to take on a protective effect for women.⁸⁸ Even the most positive trials using isolated calcium supplementation show only minor effects on bone mass. Nonetheless, a review of the research shows that calcium supplementation plus hormone replacement therapy is much more effective than hormone replacement therapy without calcium.⁸⁹ Double-blind research has found that increasing calcium intake results in greater bone mass in girls.⁹⁰ An analysis of many trials investigating the effects of calcium supplementation in premenopausal women has also shown a significant positive effect.⁹¹ Most doctors recommend calcium supplementation as a way to partially reduce the risk of osteoporosis and to help people already diagnosed with the condition. In order to achieve the 1,500 mg per day calcium intake many researchers deem optimal, 800 to 1,000 mg of supplemental calcium are generally added to the 500 to 700 mg readily obtainable from the diet.

While phosphorus is essential for bone formation, most people do not require phosphorus supplementation, because the typical western diet provides ample or even excessive amounts of phosphorus. One study, however, has shown that taking calcium can interfere with the absorption of phosphorus, potentially leading to phosphorus deficiency in elderly people, whose diets may contain less phosphorus.⁹². The authors of this study recommend that, for elderly people, at least some of the supplemental calcium be taken in the form of tricalcium phosphate or some other phosphorus-containing preparation.

One trial studying postmenopausal women combined hormone replacement therapy with magnesium (600 mg per day), calcium (500 mg per day), vitamin C, B vitamins, vitamin D, zinc, copper, manganese, boron, and other nutrients for an eight- to nine-month period.⁹³ In addition, participants were told to avoid processed foods, limit protein intake, emphasize vegetable over animal protein, and limit consumption of salt, sugar, alcohol, coffee, tea, chocolate, and tobacco. Bone density increased a remarkable 11%, compared to only 0.7% in women receiving hormone replacement alone.

Caution: Calcium supplements should be avoided by prostate cancer patients.

Taking large amounts of the combination of calcium (1,000 to 2,000 mg per day) and vitamin D has been reported to produce a marked reduction in the incidence of migraines in several women.^95,96 However, the amount of vitamin D given to these women (usually 50,000 IU once a week), can cause adverse reactions, particularly when used in combination with calcium. This amount of vitamin D should be used only under medical supervision. Doctors often recommend that people take 800 to 1,200 mg of calcium and 400 IU of vitamin D per day. However, it is not known whether theses amounts would have an effect on migraines.

Caution: Calcium supplements should be avoided by prostate cancer patients.

One double blind trial found that 1,500 mg per day of calcium improved insulin sensitivity in people with hypertension.¹⁰⁰ No research on the effects of calcium in people with metabolic syndrome has been done.

Caution: Calcium supplements should be avoided by prostate cancer patients.   

In one double-blind trial, people without depression took 600 IU of vitamin D along with 1,000 mg of calcium, or a placebo, twice daily for four weeks.¹⁰¹ Compared to the placebo, combined vitamin D and calcium supplementation produced significant elevations in mood that persisted at least one week after supplementation was discontinued.

Caution: Calcium supplements should be avoided by prostate cancer patients.

Some,¹⁰² but not all,¹⁰³ research has found that giving 500 mg of calcium twice per day for six months to people with periodontal disease results in a reduction of symptoms (bleeding gums and loose teeth). Although some doctors recommend calcium supplementation to people with diseases of the gums, supportive scientific evidence remains weak.

Caution: Calcium supplements should be avoided by prostate cancer patients.

In the past, doctors have sometimes recommended that people with a history of kidney stones restrict calcium intake because a higher calcium intake increases the amount of calcium in urine. However, calcium (from supplements or food) binds to oxalate in the gut before either can be absorbed, thus interfering with the absorption of oxalate. When oxalate is not absorbed, it cannot be excreted in urine. The resulting decrease in urinary oxalate actually reduces the risk of stone formation,¹⁰⁴ and the reduction in urinary oxalate appears to outweigh the increase in urinary calcium.¹⁰⁵ In clinical studies, people who consumed more calcium in the diet were reported to have a lower risk of forming kidney stones than people who consume less calcium.^106,107,108

However, while dietary calcium has been linked to reduction in the risk of forming stones, calcium supplements have been associated with an increased risk in a large study of American nurses.¹⁰⁹ The researchers who conducted this trial speculate that the difference in effects between dietary and supplemental calcium resulted from differences in timing of calcium consumption. Dietary calcium is eaten with food, and so it can then block absorption of oxalates that may be present at the same meal. In the study of American nurses, however, most supplemental calcium was consumed apart from food.¹¹⁰ Calcium taken without food will increase urinary calcium, thus increasing the risk of forming stones; but calcium taken without food cannot reduce the absorption of oxalate from food consumed at a different time. For this reason, these researchers speculate that calcium supplements were linked to increased risk because they were taken between meals. Thus, calcium supplements may be beneficial for many stone formers, as dietary calcium appears to be, but only if taken with meals.

When doctors recommend calcium supplements to stone formers, they often suggest 800 mg per day in the form of calcium citrate or calcium citrate malate, taken with meals. Citrate helps reduce the risk of forming a stone (see “Dietary changes that may be helpful” above).¹¹¹ Calcium citrate has been shown to increase urinary citrate in stone formers, which may act as protection against an increase in urinary calcium resulting from absorption of calcium from the supplement.¹¹²

Despite the fact that calcium supplementation taken with meals may be helpful for some, people with a history of kidney stone formation should not take calcium supplements without the supervision of a healthcare professional. Although the increase in urinary calcium caused by calcium supplements can be mild or even temporary,¹¹³ some stone formers show a potentially dangerous increase in urinary calcium following calcium supplementation; this may, in turn, increase the risk of stone formation.¹¹⁴ People who are “hyperabsorbers” of calcium should not take supplemental calcium until more is known. Using a protocol established years ago in the Journal of Urology, 24-hour urinary calcium studies conducted both with and without calcium supplementation determine which stone formers are calcium “hyperabsorbers.”¹¹⁴ Any healthcare practitioner can order this simple test.