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Supplement

Calcium

Mineral · Calcium, calcium carbonate, calcium citrate

Calcium is the building material of bones and one of the best-studied minerals of all. As a supplement, it has two strong applications: older people together with vitamin D, and pregnant women with a low-calcium diet. Added to this is a debate that has been running for years: does calcium from tablets harm the heart?

In short

Calcium keeps bones and teeth stable and is needed for muscles, nerves and blood clotting. Together with vitamin D, it lowers the risk of hip fractures in older people, to a relative risk of 0.84 in a Cochrane review with high-quality evidence and by 43 percent in a nursing home study. In pregnant women with a low-calcium diet, it markedly lowers the risk of pre-eclampsia. For younger, well-supplied people, the benefit of a supplement is barely established, and whether high doses slightly increase the risk of heart attack is disputed. The BfR recommends no more than 500 mg per day for food supplements.

What it is

Calcium is a mineral that the body incorporates mainly into bones and teeth. The EU permits the claims that calcium is needed for the maintenance of normal bones and teeth and contributes to normal muscle function and blood clotting.

The German Nutrition Society (DGE) recommends 1,000 mg per day for adults and 1,200 mg for adolescents aged 13 to 18. According to the German National Nutrition Survey, men take in a median of 1,052 mg and women 964 mg. Those below the reference value are mainly female adolescents and people aged 65 to 80. The most important sources are milk, dairy products and cheese, at about 40 percent of intake.

How it works

When calcium is lacking in the blood, the parathyroid gland releases parathyroid hormone and takes the calcium from the bone. In older people, often with additional vitamin D deficiency, this mechanism runs continuously. How directly supplements intervene here was shown by a study in female nursing home residents: with calcium and vitamin D, parathyroid hormone fell by 44 percent, and bone density at the femoral neck rose by 2.7 percent, while it fell by 4.6 percent on placebo.

Which form

Calcium carbonate contains 40 percent calcium, calcium citrate 21 percent. Carbonate therefore needs less tablet mass but more often causes bloating and constipation. Calcium from supplements is absorbed better when it is taken with a meal, and best in single doses of 500 mg or less.

The debate about the heart and blood vessels

In 2010, a group led by Bolland analyzed 15 trials of calcium without vitamin D. In the trials with patient-level data, 143 people on calcium had a heart attack, compared with 111 on placebo, a hazard ratio of 1.31. A 2021 meta-analysis of 13 double-blind trials found a 15 percent increased risk of cardiovascular disease in postmenopausal women.

Other analyses come to the opposite conclusion. A 2023 meta-analysis of 12 trials found no association with heart attack, stroke, heart failure or mortality. The National Osteoporosis Foundation and the American Society for Preventive Cardiology see no association, based on moderate-quality evidence, and consider an intake up to the upper limit of 2,000 to 2,500 mg to be cardiovascularly safe. EFSA, too, found no increased risk in 2012 at a total intake of up to 2,500 to 3,000 mg.

The BfR calls the evidence inconsistent. There is a plausible explanation for a possible risk: calcium from tablets raises the blood level more sharply and for longer than calcium from dairy products, which could promote calcification processes in blood vessels. A large cohort of 388,229 people provides an indication: dietary calcium was not associated with cardiovascular deaths there, but supplements above 1,000 mg per day in men were. How long they had been taken, however, was not known.

What is well supported

The strongest case is the combination with vitamin D in older people. A Cochrane review of 53 trials rates with high-quality evidence that vitamin D plus calcium makes hip fractures less frequent, relative risk 0.84, while vitamin D alone does not achieve this. A meta-analysis by the National Osteoporosis Foundation of 8 trials with 30,970 participants found 15 percent fewer fractures overall and 30 percent fewer hip fractures. Bone density benefits too: in a meta-analysis of 29 trials, calcium slowed bone loss at the hip by 0.54 percent and at the spine by 1.19 percent, and with high adherence there were 24 percent fewer fractures. In pregnancy, a dose of 1 g or more daily lowers the risk of pre-eclampsia, to a relative risk of 0.36 with a low-calcium diet. The WHO recommends 1.5 to 2 g daily for pregnant women in this situation. As a side effect, blood pressure falls slightly, by 1.43 mmHg systolic and 0.98 mmHg diastolic.

What the studies show

Nursing home study from France

3,270 ambulatory women with a mean age of 84 received 1.2 g of calcium and 800 IU of vitamin D3 or placebo daily for 18 months. Hip fractures were 43 percent less frequent with treatment, all nonvertebral fractures 32 percent less frequent. It shows where the combination helps most: in frail, poorly supplied older people.

Women’s Health Initiative

36,282 postmenopausal women aged 50 to 79 took 1,000 mg of calcium as carbonate and 400 IU of vitamin D3 or placebo for an average of 7.0 years. Bone density at the hip was 1.06 percent higher. Hip fractures did not decrease significantly, but they did in women who actually took their supplements, with a hazard ratio of 0.71. Kidney stones occurred more often, hazard ratio 1.17.

Cochrane review on pregnancy

27 trials with 18,064 women. A dose of 1 g or more daily lowered the risk of pre-eclampsia overall to a relative risk of 0.45, and with a low-calcium diet to 0.36. Preterm births and the combination of maternal death and serious illness also became less frequent. HELLP syndrome occurred more often, with small absolute numbers of 16 versus 6 cases.

Where the data stop

For people living independently with a normal diet, fracture protection is weak. A systematic review in the BMJ found that calcium supplements slightly lowered fractures overall, relative risk 0.89, but not hip fractures. In the 4 trials with the lowest risk of bias, with 44,505 participants combined, no effect was seen anywhere. In 44 cohort studies, dietary calcium was mostly not associated with fracture risk at all. The benefit is therefore concentrated in frail, poorly supplied older people. In pregnancy, the quality of evidence is low, the effect in adequately supplied women is not clear, and the largest single trial found only 8 percent less pre-eclampsia. Finally, the heart question remains open because the meta-analyses contradict each other. According to the BfR, systematic studies on doses below 1,000 mg per day are also lacking, that is, on exactly the amounts recommended today.

Status, approval and legal

Calcium is an authorized mineral for food supplements. The BfR proposes 500 mg per daily dose and advises that total intake from supplements should not exceed 500 mg per day. From 250 mg per daily dose, the product should carry a note not to take any other calcium-containing products. The tolerable upper intake level for total intake in adults is 2,500 mg per day, confirmed by EFSA in 2012. Calcium is not on the WADA Prohibited List for 2026.

Safety

Within normal limits, calcium is well tolerated. The most common side effects are bloating, a feeling of fullness and constipation, especially with carbonate. In the WHI, the risk of kidney stones rose with 1,000 mg daily over 7 years. The US Food and Nutrition Board therefore sets the upper limit at 2,000 mg from age 51 and considers carbonate at 3,000 mg daily problematic, especially with impaired kidney function. Very high carbonate doses can trigger milk-alkali syndrome. Calcium inhibits the absorption of levothyroxine; 4 hours should pass between the two, and 2 hours with quinolone antibiotics. With lithium, the risk of excessively high blood calcium rises. Iron absorption decreases slightly in the short term, but hemoglobin remained stable in studies. Anyone who has had kidney stones, has kidney disease or takes thyroid hormones should discuss a supplement with a physician beforehand.

BK-Score Well supported, heavily overhyped

Human evidence9
Mechanism9
Safety data9
Hype gap5
Track record of use10

For older people, the effect together with vitamin D is well supported: Cochrane rates the reduction in hip fractures (RR 0.84; 9 trials, 49,853 participants) as high-quality evidence, and in a nursing home study with 3,270 women they fell by 43 % with 44 % less parathyroid hormone (N Engl J Med 1992). In pregnancy, calcium lowers pre-eclampsia to RR 0.36 with a low-calcium diet (Cochrane 2018, low-quality evidence). For people living independently who are well supplied, the benefit is weak; the 4 trials with the lowest risk of bias showed no fracture protection (BMJ 2015). Safety is well known from large RCTs such as the WHI (36,282 women, 7.0 years), with more kidney stones (HR 1.17). On the heart, the meta-analyses contradict each other: HR 1.31 for heart attack (BMJ 2010) versus no association (Heart Lung Circ 2023; guideline Ann Intern Med 2016).

The score rates the state of knowledge, not the substance. “Safety data 9” means well studied – not harmless.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)

Frequently asked questions about calcium

How much calcium do you need per day?

The DGE recommends 1,000 mg per day for adults and 1,200 mg for adolescents. Men in Germany reach a median of 1,052 mg, women 964 mg. Anyone who eats enough dairy products usually does not need a supplement.

Are calcium tablets bad for the heart?

That is disputed. A 2010 meta-analysis found more heart attacks with calcium without vitamin D; a 2016 guideline and a 2023 meta-analysis found no association. As a precaution, the BfR recommends no more than 500 mg per day from food supplements.

Calcium carbonate or calcium citrate, which is better?

Carbonate contains 40 percent calcium and is best taken with a meal. Citrate contains 21 percent and causes constipation less often. With both, calcium is best absorbed in single doses of up to 500 mg.

Should you take calcium with vitamin D?

For older people, the combination is much better supported than calcium alone. A Cochrane review found, with high-quality evidence, fewer hip fractures with vitamin D plus calcium, while vitamin D alone had no effect.

Do pregnant women need calcium?

With a low-calcium diet, calcium at 1 g or more daily markedly lowers the risk of pre-eclampsia; the WHO then recommends 1.5 to 2 g. With adequate intake from food, the benefit is not clear. The decision belongs in prenatal care.

Can you take calcium and thyroid tablets together?

Better not. Calcium inhibits the absorption of levothyroxine; about 4 hours should pass between the two. Something similar applies to certain antibiotics, there with a gap of about 2 hours.

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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-09-26.