Do calcium supplements prevent fractures?

The meta-analysis of 59 trials finds bone density increases of 0.7 to 1.8%, small and not progressing over the years, and concludes they are unlikely to lead to a clinically significant reduction in fracture risk. A marker rising is not the same as preventing a fracture.

Is calcium from food or from a tub better?

For bone density they give practically the same: 0.6 to 1.0% a year with diet versus 0.7 to 1.8% with supplements. Since food does not carry the cardiovascular signal of supplements, food wins by elimination.

Is calcium bad for the heart?

There is a signal. In the meta-analysis of placebo-controlled trials, calcium supplements with or without vitamin D increased the risk of heart attack (RR 1.24) and the composite of heart attack or stroke (RR 1.15). It is a moderate, debated increase, but enough not to take it out of habit without need.

Calcium citrate or carbonate?

Carbonate has more calcium per milligram but needs stomach acid, so it is taken with food. Citrate is absorbed with or without food and is the practical choice for people taking stomach protectors. Absorption drops with large doses, so it is better to split them.

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Calcium · Moderate evidence

What calcium is for and how much to take

The short answer. Calcium is the bone mineral and it is needed; that is not in question. What has been measured, and rarely mentioned, is how much supplementing adds when the diet is already reasonable: a meta-analysis of 59 trials finds bone density increases of 0.7 to 1.8%, which do not progress over time and which the authors consider unlikely to meaningfully reduce fracture risk. And a separate meta-analysis finds a moderate increase in heart attack risk with supplements. The practical conclusion is boring: food first, and the tub only if food falls short.

There are studies in favour, but few, with small samples or measuring markers instead of outcomes. No figure on this page is attributed to a specific product: the effect belongs to the ingredient and every number carries its source next to it.

01 What it does and how much

Each row is a measured effect, with the figure the study gives and the source number. Where the evidence gives no figure, the column says so instead of making up a percentage.

Effects of calcium with their source
Effect	How much	Detail
Bone density with supplements	+0.7 to 1.8%	At the five skeletal sites measured, at one, two and more than two and a half years. The increase at longer timepoints was similar to the first year: it rises once and stays there. [2]
Bone density with dietary calcium	+0.6 to 1.8%	Practically the same as with supplements. Milk, yoghurt, cheese, sardines and legumes do the same job as the capsule. [2]
Fracture reduction	unlikely	That is the meta-analysis’s literal conclusion: small, non-progressive increases, unlikely to lead to a clinically significant reduction in fracture risk. [2]
Myocardial infarction	RR 1.24	In the meta-analysis of placebo-controlled trials, with data from 28,072 participants in eight trials plus the part of the Women’s Health Initiative with no prior supplement use. For the composite of heart attack or stroke, 1.15. [3]
Nutrient reference value	800 mg	The European labelling figure. It tells you how much of the daily reference a capsule covers, not that this amount has a demonstrated effect. [1]

02 How to take it

Dose. The labelling reference is 800 mg a day counting all food, not just the supplement.
When. Split rather than all at once: absorption drops in doses above 500 mg.
How long before you notice it. Bone density trials measure at one and two years.

Details that change the result

Without enough vitamin D, calcium is poorly absorbed. If something needs checking first, it is vitamin D.
Citrate is absorbed without needing stomach acid, while carbonate needs to be taken with food. For people on stomach protectors, citrate has a practical advantage.
A glass of milk, a yoghurt and a piece of cheese already add up to a large part of the daily reference. Count your food before buying.
Calcium competes with iron and zinc for absorption. Avoid taking them at the same time.

03 When it makes sense and when it does not

Worth it if

With low intake of dairy and other sources, where reaching the reference with food is not realistic.
On medical advice for osteoporosis or treatments that affect bone.
Poorly planned vegan diets, where calcium often falls short without fortified plant drinks.

Not worth it if

With a diet that already includes dairy every day: the bone density gain is the same from food as from supplements.
At high doses out of habit, given the moderate increase in heart attack risk in the meta-analyses.
Expecting it to prevent fractures on its own, which is exactly what the meta-analysis considers unlikely.

04 Sources

Every figure above comes from here. They are position stands from scientific societies, meta-analyses and peer-reviewed reviews: if a claim cannot hang from one of these lines, it is not on the page. References are cited in their original form.

Reglamento (UE) 1169/2011 sobre la informacion alimentaria facilitada al consumidor, Anexo XIII: valores de referencia de nutrientes. Calcio, 800 mg. Es un valor de ETIQUETADO, no una dosis con efecto demostrado. https://eur-lex.europa.eu/legal-content/ES/TXT/?uri=CELEX%3A32011R1169
Tai V, Leung W, Grey A, Reid IR, Bolland MJ. Calcium intake and bone mineral density: systematic review and meta-analysis. BMJ. 2015;351:h4183. Cincuenta y nueve ensayos: el calcio de la dieta aumento la densidad mineral osea un 0,6-1,0 % al ano y un 0,7-1,8 % a dos anos, y los suplementos un 0,7-1,8 % en los cinco puntos medidos, con incrementos pequenos y no progresivos que es poco probable que reduzcan de forma clinicamente significativa el riesgo de fractura. doi:10.1136/bmj.h4183
Bolland MJ et al. Calcium supplements with or without vitamin D and risk of cardiovascular events: reanalysis of the Women Health Initiative limited access dataset and meta-analysis. BMJ. 2011;342:d2040. Con datos de 28.072 participantes, los suplementos aumentaron el riesgo de infarto de miocardio (RR 1,24; IC 95 % 1,07-1,45) y del compuesto infarto o ictus (RR 1,15; IC 95 % 1,03-1,27). doi:10.1136/bmj.d2040

This is not medical advice. It is what some studies say about an ingredient, not a protocol for you. With an illness, medication or pregnancy involved, the decision belongs to a healthcare professional who knows you.

Questions about calcium

Answered with the data on this page

Do calcium supplements prevent fractures?: The meta-analysis of 59 trials finds bone density increases of 0.7 to 1.8%, small and not progressing over the years, and concludes they are unlikely to lead to a clinically significant reduction in fracture risk. A marker rising is not the same as preventing a fracture.
Is calcium from food or from a tub better?: For bone density they give practically the same: 0.6 to 1.0% a year with diet versus 0.7 to 1.8% with supplements. Since food does not carry the cardiovascular signal of supplements, food wins by elimination.
Is calcium bad for the heart?: There is a signal. In the meta-analysis of placebo-controlled trials, calcium supplements with or without vitamin D increased the risk of heart attack (RR 1.24) and the composite of heart attack or stroke (RR 1.15). It is a moderate, debated increase, but enough not to take it out of habit without need.
Calcium citrate or carbonate?: Carbonate has more calcium per milligram but needs stomach acid, so it is taken with food. Citrate is absorbed with or without food and is the practical choice for people taking stomach protectors. Absorption drops with large doses, so it is better to split them.

And now, which to buy

Prices, kept apart from the evidence

This page explains what calcium does and deliberately names no brand. The comparison is the other half: 43 products from 7 stores from €0.050 per capsule, sorted by price and by how verifiable their certification is.

See the calcium comparison

Other guides

What each supplement does, with its sources