GradedHealth

Calcium

Last reviewed October 2026 · Based on 13 studies

Bottom line

Calcium from food or supplements gives bones a small density boost, but large recent trials show little clear effect on fractures when calcium is taken alone. Trial analyses link calcium supplements to a modestly higher risk of heart attacks, so food sources may be preferable.

What it helps with

  • Builds bone density — Benefit, evidence grade B (Moderate). Meta-analysis of 59 RCTs; bone density is a surrogate for fracture, so downgraded once.
  • Prevents fractures — No effect, evidence grade B (Moderate). 2026 meta-analysis of 69 RCTs; calcium-alone result from 11 trials (about 9,000 people). Downgraded once for inconsistency with the earlier combined-supplement analysis.
  • Prevents fractures when taken with vitamin D — Mixed results, evidence grade B (Moderate). Several RCT meta-analyses that disagree: a 2026 review shows a small reduction, a 2017 analysis shows no hip fracture link, and a 2016 analysis shows a larger reduction; downgraded once for inconsistency.
  • Raises heart attack risk — Harm, evidence grade B (Moderate). Two meta-analyses of placebo-controlled trials with consistent, modest increases; cardiovascular events were secondary outcomes in the trials, so downgraded once.

What it is

Calcium is a mineral that the body uses for bone. Trials test it either as dietary calcium or as supplements such as calcium carbonate, which was given at 1,200 mg a day in one safety trial [1][2].

What the research says

Calcium from food or supplements raised bone density by about 0.6% to 1.8%, depending on the bone site and study length [1]. A 2026 review of 69 trials found calcium alone gave little to no clear change in fractures (11 trials; risk ratio 0.91, 95% confidence interval 0.81 to 1.01) [3]. Calcium with vitamin D gave a small reduction in any fracture (risk ratio 0.91, 0.84 to 0.99), but earlier reviews disagree: a 2016 analysis reported 15% fewer total fractures for calcium plus vitamin D [4][3]. Trial analyses link calcium supplements to about 24% to 31% more heart attacks, with no clear rise in stroke [5][6].

Doses used in studies

The 2015 bone review found similar bone gains at doses of 1,000 mg a day or more and at lower doses [1]. The heart analysis included placebo-controlled trials of at least 500 mg a day lasting over one year [5]. High-dose calcium in pregnancy trials was at least 1 g a day [7].

Safety and interactions

Heart attacks: calcium supplements were linked to more heart attacks in trial analyses, most clearly without vitamin D [5][6]. Kidney: calcium did not significantly raise kidney stone risk in a review of 10 studies of people with osteoporosis, though those studies were small [8]. Trials in people with kidney impairment suggest a higher cardiovascular risk [9]. Pregnancy: high-dose calcium reduced pre-eclampsia in low-quality trials, with a rise in HELLP syndrome [7]. Vitamin D: in one trial, combining calcium carbonate 1,200 mg a day with 10,000 IU of vitamin D raised the odds of high calcium in the urine 3.6-fold compared with 600 IU [2]. Our searches did not find controlled studies on the upper intake limit, common side effects or interactions with medicines, so check those with a doctor or pharmacist.

Caveats and open questions

Fracture results conflict between reviews, and the combined calcium and vitamin D results are not consistent across analyses [3][4][10]. The heart findings come mainly from secondary outcomes, not the main aims of the trials [9].

References

  1. Calcium intake and bone mineral density: systematic review and meta-analysis.. BMJ, 2015.
  2. Safety of calcium and vitamin D supplements, a randomized controlled trial.. Clin Endocrinol (Oxf), 2018.
  3. Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysis.. BMJ, 2026.
  4. Calcium plus vitamin D supplementation and risk of fractures: an updated meta-analysis from the National Osteoporosis Foundation.. Osteoporos Int, 2016.
  5. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis.. BMJ, 2010.
  6. Calcium supplements with or without vitamin D and risk of cardiovascular events: reanalysis of the Women's Health Initiative limited access dataset and meta-analysis.. BMJ, 2011.
  7. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems.. Cochrane Database Syst Rev, 2018.
  8. Calcium supplementation and kidney stone risk in osteoporosis: a systematic literature review.. Clin Exp Rheumatol, 2012.
  9. Cardiovascular effects of calcium supplementation.. Osteoporos Int, 2011.
  10. Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community-Dwelling Older Adults: A Systematic Review and Meta-analysis.. JAMA, 2017.