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The main mineral of bones and teeth, from dairy, fortified foods and supplements. Most studied for bone density and fractures, with small effects in trials.
Ask a doctor or pharmacist first if you:
Calcium is the most abundant mineral in the body, and 98% of it is stored in the bones.[1] The rest helps muscles, nerves, blood vessels and blood clotting.[1]
Milk, yogurt and cheese are rich sources. Some vegetables, canned fish with bones and fortified foods also provide it.[1] Supplements usually contain calcium carbonate or calcium citrate, and some antacids contain calcium carbonate.[1]
Large reviews found small effects of supplements on bones, and other uses have mixed or limited evidence:
Other expected benefits have little support. Calcium may make little or no difference to body weight, on low-certainty evidence.[12] In 34,157 women after menopause, calcium with vitamin D did not change sleep disturbance.[13] A later analysis of a trial in 212 people with prediabetes found better sleep with calcium only in some subgroups.[14] The evidence on leg cramps in pregnancy is unclear.[15]
Not every study of a calcium compound tests a tablet. A 2-year trial in 6,000 children, for example, tested toothpaste with arginine, a calcium compound and fluoride.[16]
Within the upper limit, most adults tolerate it, but some risks are still debated. In placebo-controlled trials reviewed by EFSA, the EU food safety authority, 2,500 mg a day from food and supplements together was tolerated without adverse effects.[17] The US upper limit is 2,500 mg a day up to age 50 and 2,000 mg from age 51.[1] The risks that are discussed most are:
People who take a medicine every day, have had kidney stones, have kidney disease or have high blood calcium should ask a doctor or pharmacist first.[1][2][3]
Almost all calcium in the body (98%) sits in the bones. A small part in the blood and tissues helps muscles, nerves, blood vessels and clotting.[1]
Each row is one benefit. The square shows the grade and the number of studies. Open a row to see the most trusted studies.
No benefit matches the filter. Clear it to see all 12.
Fracture trials in older adults gave 500 to 1,200 mg of calcium a day, often with vitamin D.[1] The US recommended amount for adults is 1,000 to 1,200 mg a day, and EFSA, the EU food safety authority, sets 950 mg from age 25.[1][22]
For bones, 500 to 1,200 mg a day with 400 to 800 IU of vitamin D.[1] For pre-eclampsia, the World Health Organization (WHO) recommends 1.5 to 2.0 g a day where intake is low, and two large trials compared 500 mg with 1,500 mg.[8][23] For premenstrual symptoms, the largest trial gave 1,200 mg a day.[10] For blood pressure, a clear effect appeared at 1,000 to 1,500 mg a day.[9]
The US recommended amount is 700 mg a day at 1 to 3 years, 1,000 mg at 4 to 8 years and 1,300 mg at 9 to 18 years. For adults it is 1,000 mg, rising to 1,200 mg for women from age 51 and for men from age 71. In pregnancy and breastfeeding it is the same as for other women of the same age.[1] EFSA sets 450 mg at 1 to 3 years, 800 mg at 4 to 10 years, 1,150 mg at 11 to 17 years, 1,000 mg at 18 to 24 years and 950 mg from age 25.[22]
The US upper limit is 2,500 mg a day for adults up to age 50 and 2,000 mg from age 51, and 3,000 mg at 9 to 18 years.[1] EFSA sets 2,500 mg a day for adults, including in pregnancy and breastfeeding, from food and supplements together.[17] People who take a medicine every day should ask a doctor or pharmacist first.[1]
Most studies gave 500 to 1,000 mg a day, for More than a year.
The counts are study groups. A study group is one set of people in a study who took the same dose. One study can have several groups. These are amounts from studies, not advice for you.
945 of 1733 study groups took calcium with something else. This shows what studies gave together, not what works together.
What studies used when they gave calcium for one goal, or to a group of people.
Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.
12 questions in 4 groups. Open one for the short answer; each has its own page with the full answer and sources.
Milk, yogurt and cheese are rich sources. Dairy products and foods with added dairy give about 72% of the calcium people get in the US.[1] Calcium in one serving:
The body absorbs about 30% of the calcium in dairy and fortified foods.[1] Spinach has 123 mg in half a cup, but only 5% is absorbed, because oxalic acid binds the calcium.[1] Broccoli, kale and cabbage have calcium that is absorbed about as well as from milk, but they have less per serving.[1]
Over years, too little calcium weakens bones and can lead to osteoporosis. It can also cause rickets in children and osteomalacia (soft bones) in children and adults, although vitamin D deficiency is the more common cause of these two.[1]
Women after menopause and people who avoid dairy, such as vegans and people with lactose intolerance or a milk allergy, are most likely to get too little.[1] In the US, 39% of people aged 4 and older get less than the estimated average requirement.[1]
A low level of calcium in the blood (hypocalcemia) usually has another cause. Examples are too little vitamin D or magnesium, a problem with parathyroid hormone, critical illness and some medicines.[1] Its most common symptoms are numbness around the mouth, tingling in the hands and feet, and muscle spasms.[1] A normal blood level does not prove a good intake, because the body keeps this level steady. A bone density scan shows calcium status over a lifetime.[1]
One trial tested supplements for rickets where the diet is very low in calcium. In 123 Nigerian children whose diets gave about 200 mg a day, 1,000 mg a day gave better healing than vitamin D alone.[7]
Probably not by much in most adults. A 2026 review of 69 trials with 153,902 people found little to no benefit from calcium, vitamin D or both on fractures and falls.[5] Evidence for people at high risk or in care homes is limited, and one trial of extra dairy foods in care homes found fewer fractures.[5][24]
The newest evidence says little or not at all. A 2025 Cochrane review found little to no difference in pre-eclampsia in large trials (risk ratio 0.92, 14,730 women).[4] Older reviews found a much larger effect, driven by small trials.[25] The World Health Organization (WHO) recommends 1.5 to 2.0 g a day where calcium intake is low.[8]
Slightly. A 2022 Cochrane review of 18 trials with 3,140 people with normal blood pressure found 1.37 mmHg lower systolic and 1.45 mmHg lower diastolic pressure.[9] The effect was larger in people under 35: 1.86 and 2.50 mmHg.[9] At 1,000 to 1,500 mg a day it was 1.05 and 2.03 mmHg.[9]
None of these trials counted how many people developed high blood pressure or reported side effects.[9] The review does not cover people who already have high blood pressure.[9] One expert review adds that blood pressure was more than 5 mmHg higher than with placebo in the hours after a large calcium dose.[26]
The DASH diet, which adds calcium from low-fat dairy, lowered blood pressure by 5.5 and 3.0 mmHg. That diet also adds potassium and magnesium, so the share due to calcium is unknown.[1]
It may, but most of the evidence has a risk of bias. In the largest trial of premenstrual symptoms, 466 women took 1,200 mg of calcium a day as carbonate or a placebo for 3 cycles. Symptoms fell by 48% with calcium and 30% with placebo.[10]
Smaller trials also found less low mood, water retention, pain and fatigue.[27][28] A pilot trial in 39 women found a much smaller effect of calcium than of fluoxetine, an antidepressant.[29] A 2025 review of 31 trials of nutrition and PMS found consistent benefits on mood symptoms with calcium, but only 1 of the 31 had a low risk of bias.[30]
For period pain, one trial in 85 students gave 1,000 mg a day from the middle of the cycle until the pain ended. Pain was 1.6 points lower than with placebo on a 10-point scale. Blood loss did not change.[31]
Not in a way that matters. A 2024 Cochrane review of 18 trials found little to no difference in body weight in people with overweight or obesity (0.15 kg less, low certainty).[12] It found that calcium probably gives small drops in body mass index (0.18 kg/m²) and waist size (0.51 cm).[12]
A 2016 review of 33 studies with 4,733 people also found no difference overall (0.01 kg). It found small losses in some subgroups, such as children and people with a normal body mass index.[32] Another review of 41 trials found no effect of supplements on weight or body fat.[1]
This is not settled. A 2021 review of 13 double-blind trials found about 15% more cardiovascular disease in healthy women after menopause.[19] A 2023 review of 12 trials found no link with heart attack, stroke or death.[20] Calcium from food does not appear to raise the risk.[26]
They may raise the risk slightly, and the evidence is mixed. In the largest trial, 36,282 women took 1,000 mg of calcium with 400 IU of vitamin D or a placebo for 7 years, and kidney stones were 17% more common with the supplement.[2] The US upper limit is based on this finding.[1]
A 2022 evidence report for the US Preventive Services Task Force also found limited evidence of a higher risk.[33] Other reviews did not. A review of 10 studies in more than 8,000 people with osteoporosis found no significant increase.[18] A review of 11 trials in 51,419 adults found no link,[1] and a 2012 opinion of EFSA, the EU food safety authority, found no established link.[17]
A diet low in calcium did not protect better. A trial in 120 men with repeated calcium oxalate stones and high urine calcium compared two diets. One had normal calcium with less animal protein and salt, and the other was low in calcium. Over 5 years, 12 men on the first diet and 23 on the second had new stones.[34]
People who have had kidney stones should ask a doctor or pharmacist before they take calcium supplements.[2]
The main ones are these, according to NIH:
Some medicines, such as bisphosphonates, cisplatin and proton pump inhibitors, can lower blood calcium.[1]
Calcium also affects iron. In a review of human studies, more calcium lowered short-term iron absorption by about 5.6%. Ferritin, a marker of iron stores, was lower at higher calcium intakes, but hemoglobin did not fall.[35] People who take a medicine every day should ask a doctor or pharmacist about calcium.[1]
Neither is clearly better for most people. Carbonate has about twice as much calcium by weight, and two studies, one of them with a light breakfast, found it as well absorbed as citrate.[1][36][37] Citrate did better in other studies, can be taken without food and appears to cause fewer stomach problems.[38][39][1]
Usually yes. Absorption of calcium supplements is greater with food, even in people with low stomach acid.[1] Calcium carbonate in particular may be absorbed poorly without a meal in people with low stomach acid. Calcium citrate can be taken without food.[1]
Taking the supplement with meals can also ease gas, bloating and constipation.[1] Oxalic acid in foods such as spinach and phytic acid in other plants bind calcium, and caffeine and phosphorus lower its absorption a little.[1]
