Calcium
An essential mineral, best known as the one taken for bones.
- Bone density
- Broken bones
- Pregnancy
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is calcium?
Calcium is a mineral the body cannot make, so all of it arrives in food — milk, cheese and other dairy are where most people get theirs. It has two quite separate jobs: it is one of the nutrients bone is built and rebuilt from, and it is the signal cells use to start and stop things, from a muscle contracting to a nerve firing. As a supplement it is always bound to a partner, usually carbonate or citrate, and that partner decides how much of each tablet is calcium itself. It is among the most widely taken supplements there is.
Why do people take calcium?
Bone density
The thinking. Bone is built and rebuilt from calcium, and bone density is the number a scan gives for how solid a bone is — the one that comes back low when someone is told their bones have thinned. Keeping that number from slipping is the oldest and commonest reason for buying calcium, usually after the menopause, or once a scan has flagged something.
What research has found. Trials have measured density at the hip, spine and forearm. Pooled supplement trials in adults over 50 showed small rises of roughly 0.7 to 1.8 per cent, which did not go on growing year after year; in premenopausal women, a review found little to no change. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
Broken bones
The thinking. Denser bone is meant to be bone that breaks less easily, so what researchers have really chased is not the scan reading but the broken wrist or hip that follows a fall. Older adults, and anyone who has already broken something, are the people most often told to take it.
What research has found. This is where the largest reviews sit: tens of thousands of adults over 50, followed for years. Across them, calcium on its own made little to no difference to hip, spine, forearm or total fractures. One earlier analysis did find a small drop in total fractures, which faded in the trials run most carefully. A fair body of trials has looked at this, and most point the same way.
Pregnancy
The thinking. Blood pressure that rises in the second half of pregnancy, with protein in the urine, is called pre-eclampsia, and it is looked for at every antenatal check. It turns up most often where diets are low in calcium, which is where this research began.
What research has found. Thirty trials covering more than 20,000 women have been pooled: calcium taken on its own roughly halved the rate of pre-eclampsia, and low doses did as well as high ones. The effect was clearest where diets were short of calcium and absent where they were not, and preterm births were fewer. One trial that stopped the tablets at 20 weeks found no clear difference. This is one of the best-studied uses, and several reviews of trials broadly agree.
What does calcium do in the body?
Calcium does two quite different jobs, and a supplement is aimed at the first. The structural job is bone: calcium is one of the nutrients a skeleton is built and repaired from. The signalling job is faster and stranger. Cells keep the calcium inside them very low, so letting a little in counts as a message — and that message is what sets a muscle contracting, a nerve firing, a cell moving or dividing.
The signalling runs on gates and pumps. Some channels in a cell’s outer wall open when the voltage across it shifts; others open when the cell’s internal store — a folded compartment called the endoplasmic reticulum — runs low. Mitochondria, the parts that make a cell’s energy, soak calcium up and release it again, helping set how fast fuel is burned and whether a worn-out cell shuts down.
What do people say about taking calcium?
These are anecdotes people have shared, not evidence.
What people like
- Very commonly it is taken as insurance for bones, especially by women from their thirties on and by anyone whose scan came back low.
- Chewable, flavoured tablets are often the ones people say they keep taking, and parents say children accept them where they will not drink milk.
- Some people were put on it by a GP, and a few mention blood results looking better afterwards, which they find reassuring.
Common complaints
- Constipation is far and away the commonest complaint, and several describe it as bad enough to make them stop or switch form.
- Stomach upset and bloating come up often, and some say chewables or citrate sit better with them than ordinary tablets.
- Several doubt the tablets do much: one reports density still worsening after years on them, and others argue food calcium is the better source.
- A minority worry about harm rather than benefit - heart and artery risk in older adults, and giving too much to young children.
How people take it
- Very commonly split through the day: posters repeat that the body takes in only about 500 mg at a time, aiming at 1,200 to 1,500 mg.
- Almost everyone pairs it with vitamin D, treated as the thing that makes it work at all; magnesium and vitamin K2 come up next.
- Carbonate is taken with food, citrate between meals, and a minority take it last thing at night; sore stomachs move people to chewables.
- Some keep it clear of other tablets - an hour away from a multivitamin, and never alongside iron, which posters say clash.
Read from these public discussions:
- Osteoporosis in forties (Mumsnet, 2024)
- Do you get your RDA of Calcium from your diet? If so, how? (Mumsnet, 2022)
- Calcium supplements for children - anyone use them and if so which ones (Mumsnet, 2006)
- Anyone take a Calcium supplement? (Cathe Friedrich fitness forums, 2005)
- Calcium supplement question (Cathe Friedrich fitness forums, 2004)
- Calcium supplements (Platelet Disorder Support Association forum)
What forms of calcium are there?
| Form | What’s different | Elemental calcium by weight | Per serving, on products we list |
|---|---|---|---|
| Carbonate | Calcium bound to carbonate, the mineral in chalk; the richest in calcium by weight of any form here. | about 40.0 % | not in our price tables yet |
| Citrate | Calcium bound to citric acid, sold as tricalcium dicitrate tetrahydrate; about half the calcium by weight that carbonate carries. | about 21.1 % | 800 mg |
| Other forms | Lactate, gluconate, citrate malate, or calcium drawn from marine algae or coral; the label states the elemental amount. | stated on the label | 1 g |
What else is worth knowing about calcium?
- Labels give the elemental calcium per serving, and a serving may be more than one tablet; the partner decides how much of a tablet’s weight is calcium — about 40 % for carbonate, about 21 % for citrate.
- Reviews of trials in adults over 50 found more kidney stones where calcium was taken with vitamin D, but no such rise where it was taken alone.
- A later pair of pregnancy trials tested 500 mg against 1,500 mg and the smaller dose held up; the World Health Organization suggests 1.5 to 2 g a day where dietary calcium is low.
- Most bone and fracture trials were in adults over 50 living at home and not on medication for thinning bones; the reviews say there is little for people in residential care.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (17 studies)
- Calcium and vitamin D for increasing bone mineral density in premenopausal women. (2023, systematic review)
- Calcium intake and bone mineral density: systematic review and meta-analysis. (2015, meta-analysis)
- Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysis. (2026, meta-analysis)
- Vitamin D, Calcium, or Combined Supplementation for the Primary Prevention of Fractures in Community-Dwelling Adults: Evidence Report and Systematic Review for the US Preventive Services Task Force. (2018, systematic review)
- Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community-Dwelling Older Adults: A Systematic Review and Meta-analysis. (2017, meta-analysis)
- Calcium intake and risk of fracture: systematic review. (2015, meta-analysis)
- Calcium for pre-eclampsia prevention: A systematic review and network meta-analysis to guide personalised antenatal care. (2022, systematic review)
- Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. (2018, meta-analysis)
- Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. (2014, meta-analysis)
- Two Randomized Trials of Low-Dose Calcium Supplementation in Pregnancy. (2024, randomised trial)
- Prepregnancy and early pregnancy calcium supplementation among women at high risk of pre-eclampsia: a multicentre, double-blind, randomised, placebo-controlled trial. (2019, randomised trial)
- Calcium and ROS: A mutual interplay. (2015, review)
- Mitochondria as sensors and regulators of calcium signalling. (2012, review)
- Store-Operated Calcium Channels. (2015, review)
- The machineries, regulation and cellular functions of mitochondrial calcium. (2018, review)
- Coronary Calcium Score and Cardiovascular Risk. (2018, review)
- The Physiology, Pathology, and Pharmacology of Voltage-Gated Calcium Channels and Their Future Therapeutic Potential. (2015, review)
How much does calcium cost?
That depends on the form and the pack, so we work out the price of the same dose of every calcium product we can find and rank them.