Calcium: How Much You Need, the Best Food Sources, and When Supplements Make Sense

Nutrition · By the Well Kept editorial team · Published 2026-10-30

White tablets spilling from a tipped-over purple bottle — Tablets spilling from a bottle: most people can get their calcium from food.

Almost all the calcium in the body is stored in the bones and teeth, and the small amount circulating in the blood is held within a narrow range because muscles, nerves and the heart depend on it. Most adults can meet their needs from food. Calcium tablets are widely sold for bone health, but the trial evidence is more nuanced than the packaging suggests, and taking more than you need has real downsides.

What calcium does

Calcium gives bones and teeth their structure. Bone is living tissue that is constantly broken down and rebuilt, and the skeleton doubles as a reserve: when dietary intake is too low, the body draws calcium from bone to keep blood levels stable. That is why a low intake does not show up in a routine blood test for a long time. The cost is paid slowly, in bone density.

Calcium is also needed for muscle contraction, the transmission of nerve signals, blood clotting and the release of hormones. The body cannot absorb it well without enough vitamin D, which is why the two nutrients are so often discussed together.

How much adults need

Official reference values differ between countries, because expert committees weigh the same research differently. None of them is a minimum below which harm begins; they are intakes set to cover the needs of nearly everyone in a group. Our guide to reading reference intakes explains how these numbers are built.

Body	Adults	Older adults	Upper limit (adults)
US National Academies (NIH ODS)	RDA 1,000 mg (19–50)	1,000 mg for men 51–70; 1,200 mg for women from 51 and everyone from 71	2,500 mg (19–50), 2,000 mg (51+)
UK (NHS)	700 mg	700 mg	The NHS says 1,500 mg or less a day from supplements is unlikely to cause harm
EFSA (EU)	PRI 1,000 mg (18–24), 950 mg (25+)	950 mg	2,500 mg

In the US, the recommended intake does not rise during pregnancy or breastfeeding for adults: the body absorbs calcium more efficiently during pregnancy, and the RDA stays at 1,000 mg.

Where calcium comes from

The NHS lists milk, cheese and other dairy foods, soya drinks with added calcium, bread and anything made with fortified flour, green leafy vegetables, and fish eaten with their bones, such as sardines and pilchards. In practice, sources fall into a few groups:

Dairy foods: milk, yoghurt and cheese are concentrated, well-absorbed sources. Hard cheeses contain very little lactose, which can help people with lactose intolerance.
Fortified foods: many plant drinks, some breakfast cereals and, in the UK, white and brown flour (by law). Fortification varies by brand and country, so the label is the only reliable guide.
Calcium-set tofu: tofu made with calcium sulphate or calcium chloride as a coagulant can be a good source; the ingredients list says which coagulant was used.
Fish with soft bones: tinned sardines, pilchards and salmon when the bones are eaten.
Vegetables, nuts and seeds: kale, pak choi, broccoli, almonds and sesame (including tahini) add useful amounts across the day.

Spinach is a common trap. It contains calcium, but also oxalate, which binds it and leaves little available for absorption. Spinach is still a nutritious vegetable; it just should not be counted on as a calcium source. Phytates in wholegrains and pulses have a smaller effect of the same kind.

Who may fall short

People who eat no dairy, including vegans and people with milk allergy, unless they choose fortified alternatives and calcium-set tofu regularly.
People with lactose intolerance who cut out dairy altogether; many tolerate small portions, yoghurt or hard cheese, and lactose-free milk keeps the calcium.
Women after the menopause, because the fall in oestrogen speeds up bone loss. This is the reason the US value rises at 51 for women.
People with conditions or treatments affecting absorption or bone, such as coeliac disease, inflammatory bowel disease or long-term oral steroids; their doctor will advise.

Our overview of who may need supplements puts calcium alongside the other nutrients these groups should watch.

Calcium supplements and fractures

For people with osteoporosis, or at high risk of it, doctors often prescribe calcium and vitamin D alongside bone-protecting medicines, particularly when dietary intake is low. That is a treatment decision, made individually.

For healthy people, the case is weaker. In 2018 the US Preventive Services Task Force recommended against daily supplementation with 400 IU or less of vitamin D and 1,000 mg or less of calcium to prevent fractures in postmenopausal women living in the community, and found the evidence insufficient for higher doses and for men. Bone health depends on much more than one mineral: weight-bearing and muscle-strengthening activity, not smoking, moderate alcohol, enough protein and vitamin D, and reducing the risk of falls in later life.

Side effects, risks and interactions

Calcium from food is not linked to the concerns raised about supplements. Supplements are different, because they deliver a large dose at once.

Digestive effects: constipation, wind and bloating are common, especially with calcium carbonate. The NHS notes that very high doses, above 1,500 mg a day, could lead to stomach pain and diarrhoea.
Kidney stones: in the large Women's Health Initiative trial, women given calcium with vitamin D had a slightly higher rate of kidney stones than those on placebo.
Heart and blood vessels: some analyses have suggested a link between calcium supplements and heart attacks, while others have not. The NIH describes the evidence as mixed; it remains a reason not to take supplements without a clear need.
High blood calcium: very high intakes, especially combined with high-dose vitamin D or with thiazide diuretics, can raise blood calcium. Our page on upper limits covers how these thresholds are set.

Calcium can also reduce the absorption of other medicines taken at the same time, including thyroid hormone (levothyroxine), some antibiotics (tetracyclines and quinolones) and bisphosphonates used for osteoporosis. A pharmacist can tell you how far apart to take them.

If you do take a supplement

Count your food first. Add up roughly what you eat on a typical day; a supplement only needs to cover the gap, not the full reference intake.
Check the form. According to the NIH, calcium carbonate is absorbed best with food, while calcium citrate is absorbed well with or without food and suits people with low stomach acid.
Split larger amounts. The NIH notes that absorption is highest in doses of 500 mg or less, so larger daily amounts are better taken in two portions.
Read the elemental calcium. Labels should state the amount of calcium itself, not just the weight of the compound.
Check for duplicates. Multivitamins, antacids and fortified foods may already supply calcium.

In short

Adults need roughly 700 to 1,200 mg of calcium a day depending on the country and on age.
Dairy, fortified plant drinks, calcium-set tofu, fish with bones and some green vegetables are the main sources.
Supplements are a treatment for some people, not a general shortcut to strong bones.
Supplements can cause constipation, slightly raise the risk of kidney stones and interact with common medicines.

This page is general information, not medical advice. If you have osteoporosis, kidney stones, a thyroid condition or take regular medicines, ask your doctor or pharmacist before taking calcium supplements.

Sources

NIH Office of Dietary Supplements, Calcium fact sheet for health professionals.
NHS, Calcium.
EFSA, Dietary reference values finder, and EFSA Panel on Dietetic Products, Nutrition and Allergies, scientific opinions on dietary reference values for calcium (2015) and on the tolerable upper intake level of calcium (2012).
US Preventive Services Task Force. Vitamin D, calcium, or combined supplementation for the primary prevention of fractures in community-dwelling adults: recommendation statement. JAMA 2018;319(15):1592–1599.
Jackson RD et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med 2006;354(7):669–683.