Supplement analysis backed by scientific evidence · PT · ES · DE · FR

← All supplements
Moderate evidenceVitamins & minerals

Calcium

Calcium supplements produce a small, one-off bump in bone density that does not keep growing with time and translates poorly into fewer fractures. Hit the target from food if you can; supplements are for people who genuinely cannot, and they carry kidney-stone and possibly cardiovascular costs.

View on iHerb Ships to 180+ countries · welcome discount for new customers

What the science says

  • Small, non-progressive increase in bone mineral density Moderate evidence

    A meta-analysis of 59 RCTs (over 12,000 participants) found calcium supplements increased BMD by 0.7-1.8% across all five measured sites, and dietary calcium by 0.6-1.8%. Crucially the increase at two-plus years was no larger than at one year — a one-time step, not a continuing gain. Increases of this size are unlikely to be clinically meaningful for fracture risk.

  • Fracture benefit is weak and probably biased Limited evidence

    A companion systematic review found dietary calcium intake was not associated with fracture risk at all, and pooled supplement RCTs gave a total fracture relative risk of 0.89 (95% CI 0.81-0.96) driven by smaller, lower-quality trials. In the large WHI trial (36,282 women on 1,000 mg calcium plus 400 IU vitamin D for seven years) the hip fracture reduction was not statistically significant.

  • Possible increase in myocardial infarction Limited evidence

    A meta-analysis of 15 trials, five with patient-level data, found calcium supplements taken without co-administered vitamin D were associated with more myocardial infarctions (pooled RR 1.27, 95% CI 1.01-1.59; patient-level HR 1.31, 95% CI 1.02-1.67). The finding is disputed and the absolute risk is small, but it does not appear with dietary calcium — which is a good reason not to supplement without need.

  • Increases kidney stone risk Moderate evidence

    In WHI, calcium plus vitamin D raised kidney stone incidence by about 17% over seven years. This is specific to supplements: dietary calcium eaten with meals actually lowers stone risk by binding oxalate in the gut, so the same mineral has opposite effects depending on how it arrives.

Dosage & safety

Studied doseRDA is 1,000 mg/day for most adults, 1,200 mg/day for women over 50 and men over 70 — counting food, which most people already partly cover. A 500-600 mg supplement usually closes the gap. Absorption falls sharply above roughly 500 mg per dose, so split anything larger. Calcium carbonate is 40% elemental calcium but requires stomach acid and must be taken with food; calcium citrate is 21% elemental but absorbs without acid, making it the choice for people on PPIs or with achlorhydria. Upper limit is 2,000-2,500 mg/day from all sources.
SafetyConstipation, bloating and flatulence are common with carbonate. Increased kidney stone risk, particularly when taken between meals. Contraindicated in hypercalcaemia and requires specialist input in primary hyperparathyroidism, sarcoidosis and other granulomatous disease. Milk-alkali syndrome can develop at high intakes combined with antacids. Calcium substantially blocks absorption of levothyroxine, bisphosphonates, tetracycline and fluoroquinolone antibiotics, and iron — separate by at least 4 hours for thyroid medication and bisphosphonates, 2 hours for the rest. Thiazide diuretics increase calcium retention and raise hypercalcaemia risk when combined with supplements.

How to take it

TimingSplit anything above 500-600 mg into separate doses — absorption falls off sharply above that per dose.
With food?Carbonate must be taken with food because it needs stomach acid; citrate absorbs without acid and can be taken any time, which makes it the choice on a PPI.
Worth knowingCount your dietary calcium first — most people need a 300-500 mg top-up, not a full 1,000 mg tablet, and taking supplements between meals raises kidney stone risk.

Interactions

With medications

  • levothyroxine

    Calcium substantially blocks absorption of thyroid hormone. separate by at least 4 hours

  • bisphosphonates (alendronate, risedronate)

    Absorption is almost abolished when taken together. take the bisphosphonate on an empty stomach and keep calcium at least 4 hours away

  • tetracycline and fluoroquinolone antibiotics

    Calcium chelates the antibiotic and reduces the dose that reaches your bloodstream. take the antibiotic at least 2 hours before or 4-6 hours after calcium

  • thiazide diuretics

    Thiazides reduce urinary calcium excretion, so combined with supplements they can push blood calcium too high. have calcium checked periodically if you use both

  • iron supplements and iron-containing medication

    Calcium competes with iron for absorption. separate by at least 2 hours

With other supplements

  • iron

    Direct absorption competition — the single most common way people undermine iron therapy. take iron in the morning and calcium at a different meal

  • zinc

    High-dose calcium modestly reduces zinc absorption. separate by a few hours if you take both

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Do calcium supplements prevent fractures?

Only weakly, if at all — the evidence is limited. Calcium supplements produce a small one-time bump in bone density of 0.7–1.8%, and the fracture benefit in trials was driven by smaller, lower-quality studies.

How much calcium per day from supplements?

Count your food first: the RDA for calcium is 1,000 mg/day for most adults, and a 300–500 mg calcium top-up usually closes the gap. Split anything above 500–600 mg, since calcium absorption falls off sharply per dose.

Should I take calcium carbonate or calcium citrate?

Calcium carbonate is 40% elemental calcium but needs stomach acid, so take it with food. Calcium citrate absorbs without acid and suits people on PPIs.

Do calcium supplements cause kidney stones?

They can — the evidence is moderate: in the WHI trial, calcium plus vitamin D raised kidney stones by about 17%. Dietary calcium eaten with meals actually lowers stone risk, and calcium supplements taken between meals are the worst option.

Scientific references

Where to buy

Nutricology, Calcium Citrate, 150 mg , 180 Vegetarian Capsules

View on iHerb

Ships to 180+ countries · welcome discount for new customers

Referral link — this site may earn a commission on purchases.

Related in Vitamins & minerals