Calcium: Roles, Food Sources, Supplements, Bone Health and Safety
Calcium's jobs in the body, food sources, official intake levels, what trials found for bones, heart and kidney stones, side effects, medicine interactions and safety.
Content last updated . This page has not been medically reviewed.
What is Calcium good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Building and keeping bones and teeth
Established roleAlmost all the calcium in your body is stored in your bones and teeth, where it keeps them strong.
Supplements: Supplements help people who do not get enough; there is no good evidence read here that extra calcium adds benefit when intake is already adequate.
Muscle contraction
Established roleCalcium helps your muscles tighten and move.
Supplements: Supplements help people who do not get enough; there is no good evidence read here that extra calcium adds benefit when intake is already adequate.
Nerve signalling
Established roleCalcium helps nerves send and receive messages.
Supplements: Supplements help people who do not get enough; there is no good evidence read here that extra calcium adds benefit when intake is already adequate.
Normal heartbeat
Established roleCalcium helps the heart muscle contract and keep a normal beat.
Supplements: Supplements help people who do not get enough; there is no good evidence read here that extra calcium adds benefit when intake is already adequate.
Blood clotting
Established roleCalcium is needed for blood to clot normally.
Supplements: Supplements help people who do not get enough; there is no good evidence read here that extra calcium adds benefit when intake is already adequate.
Blood vessel function
Established roleCalcium supports how blood vessels work.
Supplements: Supplements help people who do not get enough; there is no good evidence read here that extra calcium adds benefit when intake is already adequate.
Hormone release
Established roleCalcium helps the body release hormones.
Supplements: Supplements help people who do not get enough; there is no good evidence read here that extra calcium adds benefit when intake is already adequate.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (1)
- Bone HealthEstablished role
Calcium is needed to build and keep bones. Medical advice for osteoporosis includes enough calcium and vitamin D in the diet; whether extra supplements prevent fractures in well-nourished people is a separate question and was not verified here.
Body systems (7)
- Bones, Joints & MusclesEstablished role
Calcium keeps bones and teeth strong and helps muscles move. A role in the body is not proof that extra pills help.
- Musculoskeletal SystemEstablished role
Calcium is stored in bone and is needed for muscle contraction.
- Cardiovascular SystemEstablished role
Calcium helps the heartbeat and blood vessels work normally. This is a normal role, not proof that supplements protect the heart.
- Kidney & UrinaryDocumented risk
Higher calcium intake over a long time raises the risk of kidney stones in some people.
- Nervous SystemEstablished role
Calcium helps nerves send and receive messages.
- Urinary SystemDocumented risk
Higher calcium intake over a long time raises the risk of kidney stones in some people.
- Endocrine SystemEstablished role
Calcium helps the body release hormones.
Body parts (6)
- BonesEstablished role
Most of the body's calcium is stored in bones.
- MusclesEstablished role
Calcium helps muscles contract.
- Blood VesselsEstablished role
Calcium supports blood vessel function.
- HeartEstablished role
Calcium helps keep a normal heartbeat.
- KidneysDocumented risk
Long-term high calcium intake raises kidney stone risk in some people; kidney disease can also raise blood calcium.
- Nervous SystemEstablished role
Calcium helps nerve signals.
Functional actions (1)
- Nervous System SupportEstablished role
Calcium is part of normal nerve signalling; this does not show that supplements add benefit.
Root causes (1)
- Nutrient DeficiencyDeficiency link
Long-term low calcium intake can lead to rickets in children and osteomalacia or osteoporosis later.
Habits (1)
- Balanced NutritionEstablished role
The NHS says most people can get enough calcium from a varied, balanced diet.
Conditions & symptoms (9)
- Calcium DeficiencyDeficiency link
Too little calcium over a long time can weaken bones.
- OsteoporosisDeficiency link
Long-term low calcium intake can lead to thin, weaker bones. Enough calcium and vitamin D is part of prevention and treatment advice, alongside other measures.
- HypercalcemiaDocumented risk
High blood calcium is most often due to the parathyroid glands, but too much vitamin D, heavy calcium supplement use, kidney disease, thiazide diuretics and lithium can also raise it.
- HypocalcemiaDeficiency link
Low blood calcium has several causes, including too little calcium or vitamin D, too little magnesium, parathyroid, kidney and pancreas problems. A blood test measures it.
- Milk-Alkali SyndromeDocumented risk
MedlinePlus links it to high calcium intake from supplements together with high-dose vitamin D.
- NephrolithiasisDocumented risk
Higher calcium intake over a long time raises kidney stone risk in some people.
- OsteomalaciaDeficiency link
The NHS says too little calcium can lead to osteomalacia (soft bones) later in life.
- RicketsDeficiency link
The NHS says too little calcium can lead to rickets (soft, weak bones) in children. Vitamin D also matters.
- Lactose IntoleranceDeficiency link
People with lactose intolerance are often at higher risk of low calcium intake.
Overview
Calcium is a mineral your body needs in small amounts, and you have more of it than any other mineral. [1] Your body stores almost all of it in bones and teeth. It also helps muscles move, nerves carry messages, blood vessels move blood and hormones be released. [1] The NHS adds regulating muscle contractions, including the heartbeat, and normal blood clotting. [2]This page uses plain evidence labels. Established nutritional role means a job calcium does in the body. Mixed means trials or reviews disagree. Insufficient means the sources we read could not say. A role in the body is not proof that extra calcium from pills helps.
Food sources
- Dairy foods such as milk, cheese and yogurt are the main sources for most people in the United States. [1]
- Other sources include kale, broccoli and bok choy; canned sardines and salmon eaten with their soft bones; and calcium-enriched cereals, juices, soy and rice drinks and tofu. [1]
- MedlinePlus gives rough amounts: an 8-ounce glass of nonfat milk or calcium-fortified soy milk is about 300 mg, and 3 ounces of sardines with bones about 325 mg. [3]
- Wheat bran and foods with oxalic acid, such as spinach and rhubarb, can bind calcium and limit absorption. [3] The NHS makes the same point about spinach. [2]
For a full food list see Foods high in calcium, and for plant-based choices Dairy-free calcium.
Official intake levels
Reference intakes differ by body and country. They describe healthy groups and are not personal advice. [3]| Body, group and year | Amount |
|---|---|
| NHS (UK), adults 19 and over (page reviewed 2020) | 700 mg a day [2] |
| United States, adults 19-50; men 51-70 (MedlinePlus, 2025 review) | 1,000 mg a day (RDA) [3] |
| United States, women 51-70 and adults over 70 (MedlinePlus, 2025 review) | 1,200 mg a day (RDA) [3] |
| EU (EFSA), adults 18-24 / 25 and over (2017 summary) | 1,000 / 950 mg a day [4] |
Amounts for children, pregnancy and upper limits are on Calcium intake levels by age, sex and country.
Who may need assessment
MedlinePlus lists people who may have trouble getting enough: children and teens aged 4 to 18, people who are Black or Asian, adults 50 and older living in poverty, postmenopausal women (the body absorbs and retains less calcium) and people who do not eat dairy. [1] People with lactose intolerance are often at risk of low intake, though lactose-free milk and hard cheeses and yogurt may be options. [3] See Lactose intolerance.Deficiency and excess
A long-term lack of calcium can lead to rickets in children and osteomalacia or osteoporosis later. [2] Symptoms alone cannot show your calcium status. Low calcium in the blood is a separate medical problem: see Calcium deficiency and low blood calcium.The NHS says more than 1,500 mg a day could cause stomach pain and diarrhea, and 1,500 mg or less a day is unlikely to cause harm. [2] MedlinePlus says higher amounts over a long period raise the risk of kidney stones in some people. [3] High blood calcium can also come from an overactive parathyroid gland, too much vitamin D, kidney disease and some medicines. [5] See Too much calcium.
What the evidence says by use
| Use | What a source found | Label |
|---|---|---|
| Fracture prevention | A 2026 BMJ review of 69 trials found little to no effect of calcium alone on any fracture: risk ratio 0.91 (95% CI 0.81 to 1.01, moderate certainty). [6] | Mixed |
| Bone density | A 2015 BMJ review of trials in people over 50 found supplements raised bone density 0.7-1.8%, but the authors judged this unlikely to reduce fractures meaningfully. [7] | Mixed |
| Heart disease | A 2021 meta-analysis of placebo-controlled trials reported about 15% higher cardiovascular risk in healthy postmenopausal women. [8] | Mixed |
| Kidney stones | In the Women's Health Initiative trial, calcium (1,000 mg elemental) with vitamin D3 raised the risk of kidney stones (hazard ratio 1.17, 95% CI 1.02 to 1.34). [9] | Evidence of harm in that trial |
| Pre-eclampsia | A 2025 Cochrane review (10 trials, 37,504 participants) found calcium may make little to no difference. [10] | Insufficient |
Details are on Calcium and bone health and Calcium supplements, heart disease and kidney stones. Trials in postmenopausal women do not transfer automatically to men, children or people who eat very little calcium.
Forms and side effects
The two main supplement forms are calcium carbonate and calcium citrate. MedlinePlus says carbonate is absorbed best with food and citrate on a full or empty stomach. [1] Supplements may cause gas, bloating and constipation in some people. [1] Form comparisons are on Calcium carbonate vs citrate.Medicines and other interactions
- Ciprofloxacin: the NHS says to leave at least 2 hours between the antibiotic and dairy products or drinks with added calcium. [11]
- Levothyroxine: the NHS lists calcium and iron supplements, and antacids, among things that may not mix well with it. [12]
- Thiazide diuretics and lithium can raise blood calcium. [5]
- Alendronic acid: the NHS says not to take it with milk, and to use tap water. [13]
- Many medicines interact; ask a pharmacist before adding calcium and see Spacing supplements and medicines and Medication interactions.
Pregnancy, children, older adults, kidney and liver conditions
US reference amounts are higher for children aged 9 to 18 and for pregnant and breastfeeding teens than for adults. [3] Pregnant or breastfeeding readers should read Pregnancy and breastfeeding. People with kidney disease are among those whose blood calcium can run high, so ask a clinician first. [5] See Minerals and kidney disease. The sources we read for this page do not describe liver-specific calcium cautions; low blood protein from liver disease can lower the total calcium result. [14] Tell the surgical team about supplements before an operation: Supplements before surgery.Testing and labels
A blood calcium test measures calcium in blood, which is about 1% of the body's calcium. [14] It does not show how much calcium is in your bones; a bone density scan does. [14] Products vary in quality, so read Quality testing and certifications. Talk to a clinician or pharmacist before starting a calcium supplement. [1]Frequently asked questions
How much calcium do adults need?
It depends on the country and the age group. The NHS gives 700 mg a day for adults. [2] MedlinePlus lists 1,000 to 1,200 mg for US adults depending on age and sex. [3]
Do calcium supplements prevent fractures?
A 2026 BMJ review of 69 trials found little to no effect of calcium alone on any fracture in mostly community-dwelling adults who were not at high risk. [6] Evidence for people at high risk was limited. [6]
Are calcium supplements bad for the heart?
Some meta-analyses of trials reported more heart events with supplements, while cohort studies of dietary calcium found no effect. [8][15] The question is still debated, so talk to a clinician.
Can too much calcium cause kidney stones?
MedlinePlus says higher amounts over a long period raise stone risk in some people. [3] Calcium from food was linked to fewer stones in one large cohort of men. [16]
Can I take calcium with my other medicines?
Not always at the same time. For example, ciprofloxacin needs a gap from dairy and calcium-added drinks. [11] Ask a pharmacist.
References
- MedlinePlus, Calcium. Read 2026-10-22.
- NHS, Calcium (page last reviewed 3 August 2020). Read 2026-10-22.
- MedlinePlus Medical Encyclopedia, Calcium in diet (review date 1/21/2025). Read 2026-10-22.
- EFSA, Summary of Dietary Reference Values, version 4 (September 2017). Read 2026-10-22.
- MedlinePlus Medical Encyclopedia, Hypercalcemia. Read 2026-10-22.
- Massé O et al. BMJ 2026;393:e088050. Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysis. Read 2026-10-22.
- Tai V et al. BMJ 2015;351:h4183. Calcium intake and bone mineral density: systematic review and meta-analysis. Read 2026-10-22.
- Myung SK et al. Nutrients 2021;13(2):368. Calcium supplements and risk of cardiovascular disease: a meta-analysis of clinical trials. Read 2026-10-22.
- Jackson RD et al. N Engl J Med 2006;354(7):669-683. Calcium plus vitamin D supplementation and the risk of fractures. Read 2026-10-22.
- Cluver CA et al. Cochrane Database Syst Rev 2025;12:CD001059. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Read 2026-10-22.
- NHS, Ciprofloxacin. Read 2026-10-22.
- NHS, Levothyroxine. Read 2026-10-22.
- NHS, Alendronic acid: how and when to take it. Read 2026-10-22.
- MedlinePlus, Calcium Blood Test. Read 2026-10-22.
- Yang C et al. J Am Coll Nutr 2020;39(4):352-370. The evidence and controversy between dietary calcium intake and calcium supplementation and the risk of cardiovascular disease. Read 2026-10-22.
- Curhan GC et al. N Engl J Med 1993;328(12):833-838. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. Read 2026-10-22.