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What is calcium and what does it do?
Calcium is a mineral found in many foods. The body needs calcium to maintain strong bones and to carry out many important functions. Almost all calcium is stored in bones and teeth, where it supports their structure and hardness.The body also needs calcium for muscles to move and for nerves to carry messages between the brain and every body part. In addition, calcium is used to help blood vessels move blood throughout the body and to help release hormones and enzymes that affect almost every function in the human body.
How much calcium do I need?
The amount of calcium you need each day depends on your age. Average daily recommended amounts are listed below in milligrams (mg):
- Life Stage Recommended Amount
- Birth to 6 months 200 mg
- Infants 7–12 months 260 mg
- Children 1–3 years 700 mg
- Children 4–8 years 1,000 mg
- Children 9–13 years 1,300 mg
- Teens 14–18 years 1,300 mg
- Adults 19–50 years 1,000 mg
- Adult men 51–70 years 1,000 mg
- Adult women 51–70 years 1,200 mg
- Adults 71 years and older 1,200 mg
- Pregnant and breastfeeding teens 1,300 mg
- Pregnant and breastfeeding adults 1,000 mg
What foods provide calcium?
Milk, yogurt, and cheese are the main food sources of calcium for the majority of people in the United States.Kale, broccoli, and Chinese cabbage are fine vegetable sources of calcium.Fish with soft bones that you eat, such as canned sardines and salmon, are fine animal sources of calcium.Most grains (such as breads, pastas, and unfortified cereals), while not rich in calcium, add significant amounts of calcium to the diet because people eat them often or in large amounts.Calcium is added to some breakfast cereals, fruit juices, soy and rice beverages, and tofu. To find out whether these foods have calcium, check the product labels.
What kinds of calcium dietary supplements are available?
Calcium is found in many multivitamin-mineral supplements, though the amount varies by product. Dietary supplements that contain only calcium or calcium with other nutrients such as vitamin D are also available. Check the Supplement Facts label to determine the amount of calcium provided.The two main forms of calcium dietary supplements are carbonate and citrate. Calcium carbonate is inexpensive, but is absorbed best when taken with food. Some over-the-counter antacid products, such as Tums® and Rolaids®, contain calcium carbonate. Each pill or chew provides 200–400 mg of calcium. Calcium citrate, a more expensive form of the supplement, is absorbed well on an empty or a full stomach. In addition, people with low levels of stomach acid (a condition more common in people older than 50) absorb calcium citrate more easily than calcium carbonate. Other forms of calcium in supplements and fortified foods include gluconate, lactate, and phosphate.Calcium absorption is best when a person consumes no more than 500 mg at one time. So a person who takes 1,000 mg/day of calcium from supplements, for example, should split the dose rather than take it all at once.Calcium supplements may cause gas, bloating, and constipation in some people. If any of these symptoms occur, try spreading out the calcium dose throughout the day, taking the supplement with meals, or changing the supplement brand or calcium form you take.
Am I getting enough calcium?
Many people don't get recommended amounts of calcium from the foods they eat, including:
- Boys aged 9 to 13 years,
- Girls aged 9 to 18 years,
- Women older than 50 years,
- Men older than 70 years.
When total intakes from both food and supplements are considered, many people—particularly adolescent girls—still fall short of getting enough calcium, while some older women likely get more than the safe upper limit. See our Health Professional Fact Sheet on Calcium for more details.
Certain groups of people are more likely than others to have trouble getting enough calcium:
-Postmenopausal women because they experience greater bone loss and do not absorb calcium as well. Sufficient calcium intake from food, and supplements if needed, can slow the rate of bone loss.
-Women of childbearing age whose menstrual periods stop (amenorrhea) because they exercise heavily, eat too little, or both. They need sufficient calcium to cope with the resulting decreased calcium absorption, increased calcium losses in the urine, and slowdown in the formation of new bone.
-People with lactose intolerance cannot digest this natural sugar found in milk and experience symptoms like bloating, gas, and diarrhea when they drink more than small amounts at a time. They usually can eat other calcium-rich dairy products that are low in lactose, such as yogurt and many cheeses, and drink lactose-reduced or lactose-free milk.
-Vegans (vegetarians who eat no animal products) and ovo-vegetarians (vegetarians who eat eggs but no dairy products), because they avoid the dairy products that are a major source of calcium in other people's diets.
Some absorbed calcium is eliminated from the body in urine, feces, and sweat. This amount is affected by such factors as the following:
-Sodium and protein intakes: high sodium intake increases urinary calcium excretion [13,14]. High protein intake also increases calcium excretion and was therefore thought to negatively affect calcium status [13,14]. However, more recent research suggests that high protein intake also increases intestinal calcium absorption, effectively offsetting its effect on calcium excretion, so whole body calcium retention remains unchanged .
-Caffeine intake: this stimulant in coffee and tea can modestly increase calcium excretion and reduce absorption . One cup of regular brewed coffee, for example, causes a loss of only 2–3 mg of calcium . Moderate caffeine consumption (1 cup of coffee or 2 cups of tea per day) in young women has no negative effects on bone .
-Alcohol intake: alcohol intake can affect calcium status by reducing its absorption  and by inhibiting enzymes in the liver that help convert vitamin D to its active form . However, the amount of alcohol required to affect calcium status and whether moderate alcohol consumption is helpful or harmful to bone is unknown.
-Phosphorus intake: the effect of this mineral on calcium excretion is minimal. Several observational studies suggest that consumption of carbonated soft drinks with high levels of phosphate is associated with reduced bone mass and increased fracture risk. However, the effect is probably due to replacing milk with soda rather than the phosphorus itself [20,21].
-Fruit and vegetable intakes: metabolic acids produced by diets high in protein and cereal grains increase calcium excretion . Fruits and vegetables, when metabolized, shift the acid/base balance of the body towards the alkaline by producing bicarbonate, which reduces calcium excretion. However, it is unclear if consuming more fruits and vegetables affects bone mineral density. These foods, in addition to reducing calcium excretion, could possibly reduce calcium absorption from the gut and therefore have no net effect on calcium balance.
Many factors can affect the amount of calcium absorbed from the digestive tract, including:
- Age. Efficiency of calcium absorption decreases as people age. Recommended calcium intakes are higher for people over age 70.
- Vitamin D intake. This vitamin, present in some foods and produced in the body when skin is exposed to sunlight, increases calcium absorption.
- Other components in food. Both oxalic acid (in some vegetables and beans) and phytic acid (in whole grains) can reduce calcium absorption. People who eat a variety of foods don't have to consider these factors. They are accounted for in the calcium recommended intakes, which take absorption into account.
Can calcium be harmful?
Getting too much calcium can cause constipation. It might also interfere with the body's ability to absorb ironand zinc, but this effect is not well established. In adults, too much calcium (from dietary supplements but not food) might increase the risk of kidney stones.The safe upper limits for calcium are listed below. Most people do not get amounts above the upper limits from food alone; excess intakes usually come from the use of calcium supplements. Surveys show that some older women in the United States probably get amounts somewhat above the upper limit since the use of calcium supplements is common among these women.
- Life Stage Upper Safe Limit
- Birth to 6 months 1,000 mg
- Infants 7–12 months 1,500 mg
- Children 1–8 years 2,500 mg
- Children 9–18 years 3,000 mg
- Adults 19–50 years 2,500 mg
- Adults 51 years and older 2,000 mg
- Pregnant and breastfeeding teens 3,000 mg
- Pregnant and breastfeeding adults 2,500 mg
Are there any interactions with calcium that I should know about?
Calcium dietary supplements can interact or interfere with certain medicines that you take, and some medicines can lower or raise calcium levels in the body. Here are some examples:
- - Calcium can reduce the absorption of these drugs when taken together:
- * Bisphosphonates (to treat osteoporosis)
- * Antibiotics of the fluoroquinolone and tetracycline families
- * Levothyroxine (to treat low thyroid activity)
- * Phenytoin (an anticonvulsant)
- * Tiludronate disodium (to treat Paget's disease).
- - Diuretics differ in their effects. Thiazide-type diuretics (such as Diuril® and Lozol®) reduce calcium excretion by the kidneys which in turn can raise blood calcium levels too high. But loop diuretics (such as Lasix® and Bumex®) increase calcium excretion and thereby lower blood calcium levels.
- Antacids containing aluminum or magnesium increase calcium loss in the urine.
- Mineral oil and stimulant laxatives reduce calcium absorption.
- Glucocorticoids (such as prednisone) can cause calcium depletion and eventually osteoporosis when people use them for months at a time.