Other name(s):

calcium carbonate, calcium citrate, calcium glubionate, calcium gluconate, calcium lactate, calcium phosphate, tricalcium phosphate

General description

Calcium is the most abundant mineral in the human body. It makes up the main part of bone. This mineral is also needed for blood vessels to contract and dilate, and for many muscle functions. It helps send nerve impulses and control nerve irritability. It also helps to clot blood. Calcium is also an enzyme cofactor It aids the function of the endocrine and exocrine glands.

One of the important forms of calcium is called calcium hydroxyapatite. This type of calcium is a building block of bone and tooth enamel.

Medically valid uses

Calcium is of extra importance in times of bone growth. These include childhood and the teen years. It’s also extremely important during pregnancy, when breastfeeding, and after menopause.

You need calcium to make breastmilk. A baby in the uterus also needs it to grow.

Not getting enough calcium in puberty and adulthood may lead to osteopenia and osteoporosis. These conditions cause weak bones that may break easily.

Unsubstantiated claims

There may be additional benefits to calcium that have not yet been proven through research.

Calcium may lower the risk of colorectal and prostate cancer. It may also help reduce the risk of heart disease and may lower blood pressure. It may also ease menstrual cramps and help manage weight. Calcium may help to prevent preterm labor and birth.

Recommended intake

Calcium is measured in milligrams (mg). It’s absorbed by the small intestine. But only part of the calcium in foods and supplements is absorbed.

The recommended dietary allowance (RDA) by age is:



Infants (0 to 6 months)

200 mg

Infants (6 months to 1 year)

260 mg

Children (1 to 3 years)

700 mg

Children (4 to 8 years)

1,000 mg

Youth (9 to 18 years)

1,300 mg

Adults (females 19 to 50 years; males 19 to 70 years)

1,000 mg

Adults (70+ years)

1,200 mg


50 years and older

1,200 mg

Pregnant or lactating, 18 years or younger

1,300 mg

Pregnant or lactating, 19 to 50 years

1,000 mg

Calcium in supplements most often comes in two forms. These are carbonate and citrate. Calcium carbonate needs stomach acid to be absorbed. It should be taken with food. Calcium citrate is more easily absorbed. It can be taken with or without food. People with low stomach acid should take this kind. This includes older adults.

Calcium is available in oral tablets. Doses range from 250 to 1,200 mg. It also comes as oral chews, capsules, powders, wafers, and liquids. Your body absorbs calcium the best when the dose is 500 mg or less at one time. That means if you want to get 1000 mg a day, take two 500-mg doses at separate times of the day. Vitamin D helps your body absorb calcium.

Calcium exists in nature only with other substances called compounds. These compounds contain different amounts of elemental calcium. This is the actual amount of calcium in the supplement. Calcium is found in many products. Each form has a different amount of calcium. Calcium carbonate and calcium phosphate have the highest amounts of calcium. Calcium gluconate and calcium glubionate have the lowest.

Calcium-rich foods


Calcium (mg)

Fortified oatmeal, 1 packet


Sardines, canned in oil, with edible bones, 3 ounces


Cheddar cheese, shredded, 1.5 ounces


Milk, nonfat, 1 cup


Milkshake, 1 cup


Yogurt, plain, low-fat, 1 cup


Soybeans, cooked, 1 cup


Tofu, firm, with calcium, 1/2 cup


Orange juice, fortified with calcium, 6 ounces


Salmon, canned, with edible bones, 3 ounces


Pudding, instant (chocolate, banana, etc.) made with 2% milk, 1/2 cup


Baked beans, 1 cup


Cottage cheese, 1% milk fat, 1 cup


Spaghetti, lasagna, 1 cup


Frozen yogurt, vanilla, soft-serve, 1/2 cup


Ready-to-eat cereal, fortified with calcium, 1 cup


Cheese pizza, 1 slice


Fortified waffles, 2


Turnip greens, boiled, 1/2 cup


Broccoli, raw, 1 cup


Ice cream, vanilla, 1/2 cup


Soy or rice milk, fortified with calcium, 1 cup

80–500 (varies)

Calcium is stable in foods. It doesn’t break down with storage or cooking.

You may need more calcium if you have any of these:

  • A malabsorption syndrome, such as sprue or celiac disease

  • Pancreatitis

  • Cirrhosis of the liver

  • Lactose intolerance

  • Milk allergies

  • Anorexia

  • A vegetarian diet that doesn’t include eggs or dairy

  • Moderate to heavy alcohol or caffeine intake

  • Long-term use of corticosteroids

Calcium is absorbed best by the body when it’s taken several times a day in amounts of 500 mg or less. But taking it all at once is better than not taking it at all. Calcium carbonate is absorbed best when taken with food. Calcium citrate can be taken anytime.

Calcium supplements are used to treat calcium-deficiency problems. These include:

  • Tetany

  • Kidney problems, including end-stage kidney disease

  • Thyroid issues

  • Osteoporosis and softening of the bone (osteomalacia)

  • Rickets

Chronic calcium deficiency leads to poor bone mineralization. It also causes decreased bone growth and repair. In young adults, this may lead to osteomalacia. In older adults and postmenopausal women, it may lead to osteoporosis. In children, it’s linked with rickets. This is often due to both vitamin D and calcium deficiency.

Tetany occurs when the serum level of ionized calcium becomes too low. This causes muscles to contract and stay contracted. This condition happens due to an acute decrease in ionized calcium in the blood. It’s often a result of hyperventilation.

Side effects, toxicity, and interactions

High levels of calcium in the blood is called hypercalcemia. This rarely happens from eating too much calcium from foods. It’s more likely to be caused by calcium supplements. Too much calcium from supplements may also cause kidney stones.

Excess calcium intake (2 grams or more per day) may cause calcium deposits in muscles. This may cause stiffness and pain. Calcium deposits can also show up on heart valves. This can cause fatal heart damage. Calcium deposits are more likely to happen when you also have a high vitamin D intake. Be careful not to take more than 800 mcg/day of vitamin D without your healthcare provider's recommendation, especially when taking calcium supplements.

Consuming large amounts of calcium with milk or an antacid can cause milk-alkali syndrome. This can cause hypercalcemia. It can also harm your kidneys.

You shouldn’t take calcium supplements if any of the below apply to you:

  • Your serum calcium levels are too high

  • Your phosphate levels are too low

  • You have kidney failure

  • You plan to have dialysis

  • You are taking thiazide diuretics, such as HCTZ, hydrochlorothiazide, or indapamide

  • You get kidney stones

Women who are pregnant or breastfeeding should talk to their healthcare providers before taking any supplements.

Calcium also interacts with certain medicines. These include:

  • Tetracycline antibiotics

  • Norfloxacin

  • Verapamil

  • Levothyroxine

Calcium also reduces how well the body absorbs iron. You shouldn’t take calcium at the same time as iron. You can do so if the calcium is calcium citrate, or if you take the iron with vitamin C. You shouldn’t take any medicine that needs to be taken on an empty stomach with calcium supplements. Calcium limits the absorption of magnesium, iron, and zinc. High levels of vitamin D may cause you to absorb more calcium.

Additional information

Calcium is the most commonly used supplement. It’s the easiest one to use. It also helps prevent osteoporosis.

Over 40 million people in the U.S. have osteoporosis or have a high risk for the condition. These factors increase the risk for osteoporosis in women:

  • Being thin or underweight

  • Having an eating disorder, such as anorexia nervosa

  • Chronic dieting

  • High alcohol or caffeine intake

  • A diet lacking in calcium

Keeping a healthy weight during the teen years can help prevent osteoporosis as an adult. Getting regular exercise can also help. Choose high impact activities, such as running or lifting weights.

Women who get their first menstrual period at a younger age or go through menopause at a later age have a lower risk of osteoporosis. Making sure you get enough calcium and vitamin D throughout your life can also lower your risk of the condition.

Online Medical Reviewer: Bianca Garilli MD
Online Medical Reviewer: Chris Southard RN
Online Medical Reviewer: Stacey Wojcik MBA BSN RN
Date Last Reviewed: 8/1/2023