Minerals · 4 min read ·

Calcium: for bones, but not from tablets at any cost

Calcium is the main building block of bones. How much the body takes from food depends on the food and on the dose — and supplements have their risks.

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In a nutshell

1What it does and how much you need

About 99% of the body’s calcium is in bones and teeth; the remaining 1% acts as a signal in cells. When the diet does not provide enough, the body takes calcium from the bones to keep the blood level steady — bone is lost and the risk of fractures rises.1

EFSA recommendation 950 mg EFSA recommends 950 mg of calcium a day for adults from age 25 and 1,000 mg for young adults (18–24), because their bones are still getting stronger. The same values apply in pregnancy and breastfeeding.1

2Where to find it

Data 1,184 mg Hard cheeses have the most calcium (Parmesan 1,184 mg per 100 g, Emmental 890 mg), followed by sesame (975 mg) and firm tofu (683 mg). Then dairy, sardines with bones, pulses, nuts and dark green vegetables; hard water contributes too.1,3

3How much is absorbed

Weak evidence — absorption studies 64% → 29% The more calcium at once, the smaller the share absorbed: in a study of women, 64% was absorbed from small doses (15 mg) but only 28.6% from 500 mg.4
Weak evidence — small studies 5% / 28% / 41% Only 5% of calcium was absorbed from spinach, 28% from milk in the same study. From kale 41%, more than from milk in the comparison study (32%). Calcium bound to oxalic acid was absorbed only 10%.5,6,7
Moderate evidence +22–27% A summary of 15 studies: 22–27% more calcium was absorbed from calcium citrate than from carbonate, both fasting and with meals.8

In the EU, supplements may contain calcium in many forms, including carbonate, citrate, citrate malate, gluconate, lactate, phosphates or calcium bisglycinate.9 Vitamin D supports calcium absorption.1

4Supplements: bones, heart and kidneys

Strong evidence +0.7–1.8% A summary of 59 randomised trials in people over 50: more calcium from food or supplements raised bone density by only 0.7–1.8%. According to the authors, this is too little to markedly reduce the risk of fractures.10
Moderate evidence −11% A summary of studies in people over 50: calcium from food was not linked to fracture risk. Supplements reduced total fractures by 11% in randomised trials, but had no effect in the best-quality trials.11
Moderate evidence +27–31% A summary of randomised trials: people taking calcium supplements without vitamin D had 27–31% more heart attacks than with placebo.12
Moderate evidence — a large randomised trial +17% In the WHI trial of 36,282 post-menopausal women, 1,000 mg of calcium with vitamin D a day raised the risk of kidney stones by 17%. Hip fractures did not decrease significantly.13
Upper level 2,500 mg The upper level is 2,500 mg of calcium a day from all sources. EFSA concluded that a link between long-term calcium intake and kidney stones, heart disease or prostate cancer has not been established.2

What to take from this

Sources

Written on , based on studies available at that date. Newer research may change the conclusions.

  1. EFSA NDA Panel (2015). Scientific Opinion on Dietary Reference Values for calcium. EFSA Journal 13:4101. doi.org/10.2903/j.efsa.2015.4101
  2. EFSA NDA Panel (2012). Scientific Opinion on the Tolerable Upper Intake Level of calcium. EFSA Journal 10:2814. doi.org/10.2903/j.efsa.2012.2814
  3. USDA ARS (2018). FoodData Central — SR Legacy, calcium per 100 g: parmesan 1,184 mg (FDC 170848), sesame seeds 975 mg (FDC 170150), swiss cheese (Emmental) 890 mg (FDC 171251), firm tofu 683 mg (FDC 172475), sardines in oil, drained 382 mg (FDC 175139). fdc.nal.usda.gov
  4. Heaney R. P., Weaver C. M., Fitzsimmons M. L. (1990). Influence of calcium load on absorption fraction. J Bone Miner Res 5:1135–1138. doi.org/10.1002/jbmr.5650051107
  5. Heaney R. P., Weaver C. M., Recker R. R. (1988). Calcium absorbability from spinach. Am J Clin Nutr 47:707–709. doi.org/10.1093/ajcn/47.4.707
  6. Heaney R. P., Weaver C. M. (1990). Calcium absorption from kale. Am J Clin Nutr 51:656–657. doi.org/10.1093/ajcn/51.4.656
  7. Heaney R. P., Weaver C. M. (1989). Oxalate: effect on calcium absorbability. Am J Clin Nutr 50:830–832. doi.org/10.1093/ajcn/50.4.830
  8. Sakhaee K. et al. (1999). Meta-analysis of calcium bioavailability: a comparison of calcium citrate with calcium carbonate. Am J Ther 6:313–321. doi.org/10.1097/00045391-199911000-00005
  9. Directive 2002/46/EC on food supplements, Annex II — forms of vitamins and minerals permitted in supplements (consolidated version 26 Nov 2025). eur-lex.europa.eu
  10. Tai V. et al. (2015). Calcium intake and bone mineral density: systematic review and meta-analysis. BMJ 351:h4183. doi.org/10.1136/bmj.h4183
  11. Bolland M. J. et al. (2015). Calcium intake and risk of fracture: systematic review. BMJ 351:h4580. doi.org/10.1136/bmj.h4580
  12. Bolland M. J. et al. (2010). Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ 341:c3691. doi.org/10.1136/bmj.c3691
  13. Jackson R. D. et al. (2006). Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med 354:669–683. doi.org/10.1056/NEJMoa055218

This is general information and does not replace a doctor. Have kidney stones or heart disease? Talk to a doctor about calcium supplements.