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Calcium

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’s the main part of bone. But it is also needed for blood vessels to contract and dilate, and for 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 endocrine and exocrine glands. Most calcium is a building block of bone and tooth enamel. This is called calcium hydroxyapatite.

Medically valid uses

Calcium is extra important in times of bone growth. These include childhood and adolescence. It’s also needed during pregnancy, when breastfeeding, and after menopause.

You need calcium to make breast milk. A baby in the womb 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 benefits that have not yet been proven through research.

Calcium may lower the risk of colorectal cancer. It may also help reduce the risk of heart disease. It 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:

Group

RDA

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

 Women

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 come in 2 forms. These are carbonate and citrate. Carbonate needs stomach acid to be absorbed. It should be taken with food. 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 500mg or less at 1 time. That means if you want to get 1000mg a day, take 2 500mg doses at separate times of 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

Food

Calcium (mg)

Fortified oatmeal, 1 packet

350

Sardines, canned in oil, with edible bones, 3 oz.

324

Cheddar cheese, 1.5 oz. shredded

306

Milk, nonfat, 1 cup

302

Milkshake, 1 cup

300

Yogurt, plain, low-fat, 1 cup

300

Soybeans, cooked, 1 cup

261

Tofu, firm, with calcium, 1/2 cup

204

Orange juice, fortified with calcium, 6 oz.

200–260

Salmon, canned, with edible bones, 3 oz.

181

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

153

Baked beans, 1 cup

142

Cottage cheese, 1% milk fat, 1 cup

138

Spaghetti, lasagna, 1 cup

125

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

103

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

100–1,000

Cheese pizza, 1 slice

100

Fortified waffles, 2

100

Turnip greens, boiled, 1/2 cup

99

Broccoli, raw, 1 cup

90

Ice cream, vanilla, 1/2 cup

85

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 the below:

  • 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

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 of the newborn

  • 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 post-menopausal 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. 

Excess calcium intake (2 grams or more) may cause calcium deposits in muscles. This may cause stiffness and pains. 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, 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

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 adolescence 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: Cynthia Godsey
Online Medical Reviewer: Diane Horowitz MD
Online Medical Reviewer: Rita Sather RN
Date Last Reviewed: 8/1/2016