Quick answer

Calcium is the mineral that gives bones and teeth their structure, and muscles, nerves and blood vessels need it to work. Adults need 1,000 to 1,200 mg a day from food and supplements combined. The body absorbs supplements best at 500 mg or less at a time, and total intake should stay under 2,000 to 2,500 mg.^1,2

Key facts

Adults need 1,000 mg of calcium a day; women from 51 and men from 71 need 1,200 mg.¹
The Daily Value on supplement labels is 1,300 mg, so a label's percentage is a share of that figure.²
Lactose-free milk and yogurt contain the same calcium as regular dairy.²
Calcium can lower the absorption of levothyroxine, some antibiotics and bone medicines such as alendronate.^1,3

What calcium does in the body

About 98% of the body's calcium is in the bones, which act as a reserve the body draws on to keep the level in the blood steady.²

The body needs vitamin D to absorb calcium through the main active route in the gut and to keep blood calcium in range.^1,2

Outside the skeleton, a small amount of calcium circulates in the blood and the fluid around cells. It lets blood vessels tighten and relax, muscles contract, blood clot, nerves pass signals and glands release hormones. Bone is not fixed: it is broken down and rebuilt all the time, which lets the body move calcium in and out as needed.²

What the evidence shows

Each claim below carries a grade and the amount the studies used. Calcium's roles in the body are well established. What supplements add for people who already eat enough is small, and the bone density gains seen in trials did not build up over time.^2,4

Needed to build and maintain bones and teeth*^1,2

Moderate evidence

A long-established role of the mineral, described by NIH. About 98% of the body's calcium sits in the skeleton, and the recommended amounts for adults were set at the intake needed to maintain bone. The skeleton is also the reserve the body draws on to keep blood calcium steady, so a shortfall shows up in bone over years rather than in a blood test.

Amount studied: Recommended intake: 1,000 mg a day for most adults, 1,200 mg for women over 50 and everyone over 70

Helps you reach the recommended daily calcium intake when food falls short*²

Moderate evidence

National survey data from 2007 to 2010 show that 39% of people aged 4 and older get less calcium than the estimated average requirement from food and supplements, including 49% of children aged 4 to 18. Women average 842 mg a day from food alone; counting supplements, their average rises to 1,009 mg, close to the 1,000 to 1,200 mg they need.

Amount studied: Recommended intake: 1,000 to 1,200 mg a day for adults, from food and supplements combined

Produces small gains in bone mineral density in adults over 50*^2,4,5

Moderate evidence

A meta-analysis of 51 randomized trials of calcium supplements in 12,257 people over 50 found bone density 0.7% to 1.8% higher at five skeletal sites, with similar gains from extra dietary calcium. The gain appeared within a year and did not grow after that; it was similar with or without vitamin D and at higher or lower doses, and the authors judged it too small to be likely to matter clinically. In the Women's Health Initiative, 1,000 mg of calcium with vitamin D a day left hip bone density 1.06% higher after about 7 years.

Amount studied: Calcium supplements from under 500 mg to over 1,000 mg a day, with or without vitamin D, for one to several years

Contributes to normal muscle contraction, nerve signaling, blood clotting and the release of hormones*^1,2

Moderate evidence

A well-established role, described by NIH: a small pool of calcium in blood and tissues lets blood vessels contract and relax, muscles work, blood clot, nerves send signals and glands release hormones. The body keeps this pool in a tight range by drawing on bone when intake is low, which is why blood calcium says little about how much calcium a person eats.

Amount studied: Recommended daily intake from food and supplements

How much calcium you need

Calcium per day, from food and supplements^1,2
Who	Recommended	Upper limit
Adults 19 to 50	1,000 mg	2,500 mg
Men 51 to 70	1,000 mg	2,000 mg
Women 51 to 70	1,200 mg	2,000 mg
Adults over 70	1,200 mg	2,000 mg
Teens 14 to 18	1,300 mg	3,000 mg
Pregnant or breastfeeding, 19 and older	1,000 mg	2,500 mg

The body absorbs calcium best in amounts of 500 mg or less at a time. Someone taking 1,000 mg a day from supplements does better with two smaller doses than one large one.^1,2

Both columns count food and supplements together. The dosage guide shows how much a typical day's food already provides, so you can work out whether a supplement is needed at all.²

Who is most likely to fall short

NIH lists these groups as more likely than others to get too little calcium:¹

Children and teens aged 4 to 18¹
Women after menopause, who absorb and keep less calcium¹
People who eat no dairy, including vegans¹
Black and Asian Americans, and adults over 50 living on low incomes, in national survey data¹

Food sources

Milk, yogurt and cheese are the main sources of calcium in the US: dairy products and foods made with them supply about 72% of the calcium Americans eat.^1,2

Canned sardines and salmon with the bones, kale, broccoli and Chinese cabbage also provide calcium, and many fruit juices, soy and almond drinks, tofu and cereals have calcium added.^1,2

Most grains, such as bread and pasta, are low in calcium, but they add up because people eat them often. Some juices are fortified with calcium citrate malate, a form the body absorbs well.^1,2

Supplement forms

Calcium carbonate is 40% calcium by weight and is absorbed best when taken with food. It is also the calcium in many antacids.^1,2

Calcium citrate is 21% calcium by weight and depends less on stomach acid, so it is absorbed well with or without food. People with low stomach acid, which is most common in older adults, absorb it more easily than carbonate.^1,2

Other forms in supplements and fortified foods include calcium sulfate, ascorbate, gluconate, lactate, phosphate and microcrystalline hydroxyapatite. Whatever the form, the Supplement Facts panel lists the calcium itself, so amounts can be compared directly.^1,2

Side effects, limits and medicines

Calcium supplements can cause gas, bloating, constipation or a mix of these. Carbonate causes them more often than citrate, especially in older adults with less stomach acid; smaller doses spread through the day, taking it with meals or switching forms can help.^1,2

The upper limit for calcium from food and supplements combined is 2,500 mg a day for adults aged 19 to 50 and 2,000 mg from age 51. For children aged 9 to 18 it is 3,000 mg.^1,2

The upper limit was set after a large trial recorded more kidney stones in women taking calcium with vitamin D, and research on calcium supplements and the heart is mixed. The side effects guide covers both.^2,5