Calcium is the most abundant mineral in the body. It is essential for the development and maintenance of strong bones and teeth, the location of about 99% of the body's calcium. Calcium also helps the heart, nerves, muscles, and other body systems work properly. It is probably best known for its effects in preventing osteoporosis. Your body needs several other nutrients in order for calcium to be absorbed and used properly, including magnesium, phosphorous, and especially vitamins D and K.

The best way to get calcium is through food (see Dietary Sources). But although many foods are fortified with calcium, some people may still need to take calcium supplements. In fact, according to the National Institutes of Health, many Americans consume less than half the amount of calcium recommended to build and maintain healthy bones. It is especially important to get enough calcium as you age. Postmenopausal women, people who consume large amounts of caffeine, alcohol, or soda, and those who take corticosteroid medications may need calcium supplements. Calcium deficiency can be found in people with malabsorption problems, such as Crohn's disease, celiac disease, and surgical intestinal resection.

Getting enough calcium can help prevent or treat the following conditions:

Osteoporosis

Calcium is necessary to help build and maintain healthy bones and strong teeth. Studies have shown that calcium, particularly in combination with vitamin D, can help prevent bone loss associated with menopause, as well as the bone loss experienced by older men. If you do not get enough calcium in your diet, taking a supplement may be necessary.

Hypoparathyroidism

People with this condition have underactive parathyroid glands, which are four small glands that sit on the four corners of the thyroid in the neck and produce a hormone that regulates calcium, phosphorous, and vitamin D levels in the body. People with this condition should follow a high-calcium, low-phosphorous diet as prescribed by their doctor. Most often, they will also need to take calcium supplements.

Premenstrual Syndrome (PMS)

One large, well-designed study showed that women who took 1,200 mg of calcium per day reduced their symptoms of PMS by 50%, including headache, moodiness, food cravings, and bloating. A smaller study suggested that calcium may help reduce menstrual pain.

High Blood Pressure

People who do not get enough calcium may be at higher risk for hypertension, and there is some mixed evidence that suggests increasing calcium levels may lower blood pressure slightly. However, not all studies have found that benefit; and researchers aren’t sure whether calcium supplements would have any benefit, or whether it’s the effects of a diet that includes low-fat dairy products (which contain calcium) that is responsible. If you want to try calcium supplements, do not stop taking your blood pressure medication; talk to your doctor and let the doctor determine the proper dose of calcium for you. You may need to take calcium for 6 - 8 weeks before you see any improvement in blood pressure.

Some studies suggest that calcium supplementation may play a role in the prevention of pregnancy-induced high blood pressure and preeclampsia (a combination of high blood pressure, fluid retention, and high levels of protein in the urine that some women develop in the last trimester of pregnancy). However, not all studies show the same benefit. A prenatal vitamin, which provides magnesium, folic acid, and many other nutrients, together with adequate calcium intake through the diet, may lower the risk of developing high blood pressure during pregnancy.

Obesity

Some animal and human studies have found that consuming low-fat dairy products may help you lose or maintain a proper weight. However, researchers aren’t sure whether the calcium in the dairy products affects weight, some other nutrient -- or even a combination of nutrients. In addition, not all studies have found any benefit; and there’s no sound evidence that calcium supplements (as opposed to dairy products) would help in losing weight. More research is needed.

High Cholesterol

Preliminary studies in animals and people suggest that calcium supplements, in the range of 1,500 to 2,000 mg per day, may help to lower cholesterol slightly. From these studies, it appears that calcium supplements (along with exercise and proper diet) may be better at keeping cholesterol at normal levels than at lowering them once cholesterol is already high. More research in this area is needed.

Rickets

Rickets causes softening and weakening of the bone in children. Although virtually eliminated in North America and Western Europe, where milk consumption is common, it still occurs in many parts of the world. Researchers have thought that rickets is caused by a lack of vitamin D; however, a study in 2000 showed that calcium supplementation is an effective treatment.

Other Uses

Stroke -- In a population-based study (one in which large groups of people are followed over time), women who take in more calcium, both through their diet and with supplements, were less likely to have a stroke over a 14-year period. More research is needed.

Colon Cancer -- Although not all studies agree, some show that people who consume higher amounts of calcium, vitamin D, and milk in their diets are less likely to develop colorectal cancer than those who consume low amounts of the same nutrients. But researchers are not sure whether calcium supplements would have the same effect as calcium in the diet, or even whether calcium itself is responsible for the benefit.

The richest dietary sources of calcium include cheeses (such as parmesan, Romano, gruyere, cheddar, American, mozzarella, and feta), low-fat dairy products (milk, yogurt), tofu, and blackstrap molasses. Some other good sources of calcium include almonds, brewer's yeast, bok choy, Brazil nuts, broccoli, cabbage, dried figs, kelp, dark leafy greens (dandelion, turnip, collard, mustard, kale, Swiss chard), hazelnuts, oysters, sardines, and canned salmon,.

Foods that are fortified with calcium, such as juices, soy milk, rice milk, tofu and cereals, are also good sources of this mineral.

There are a number of forms of calcium available as dietary supplements. They differ in the amount of calcium they contain, how well they are absorbed by the body, and how much they cost. The two most popular forms are calcium citrate and calcium carbonate.

• Calcium citrate: Easily absorbed and digested by the body, particularly in the elderly. It does not contain as much elemental calcium (the amount your body actually absorbs) as calcium carbonate. It is more costly than calcium carbonate, however. Also, calcium citrate should not be used with aluminum-containing antacids (see Possible Interactions).
• Calcium carbonate: Less expensive than calcium citrate and contains more elemental calcium. Requires a certain amount of stomach acid to be absorbed, so it is usually taken with a glass of orange juice. Many antacids contain calcium carbonate.

Calcium supplements that are derived from oyster shells, dolomite, and bone meal are best avoided as they may contain lead, a toxic metal (particularly worrisome in children and those with kidney disease) that can harm the brain and kidneys, cause anemia, and raise blood pressure.

Calcium supplements should be taken in small doses (no more than 500 mg at a time -- that’s all your body can absorb in one dose) throughout the day with 6 - 8 cups of water to avoid constipation.

The following are daily dietary recommendations for general health and prevention of disease.

Pediatric

Talk to your pediatrician before giving a child any nutritional supplement.

• Infants birth to 6 months: 210 mg
• Infants 7 months to 1 year: 270 mg
• Children 1 - 3 years: 500 mg
• Children 4 - 8 years: 800 mg
• Adolescents 9 - 18 years: 1,300 mg

Adult

• 19 - 50 years: 1,000 mg
• 51 years and older: 1,200 mg
• Pregnant and breastfeeding females under 19 years: 1,300 mg
• Pregnant and breastfeeding females 19 years and older: 1,000 mg

For prevention of colon cancer, 1,800 mg per day may be required.

Because of the potential for side effects and interactions with medications, dietary supplements should be taken only under the supervision of a knowledgeable health care provider. Total calcium intake, from combined dietary and supplemental sources, should not exceed 2,500 mg per day.

Side effects can include constipation and stomach upset. Very high doses can cause nausea, vomiting, loss of appetite, increased urination, kidney toxicity, confusion, and irregular heart rhythm.

More generally, such high levels of calcium in the body occur when the body produces too much calcium. People with hyperparathyroidism, kidney failure, sarcoidosis, or cancer could be at risk for elevated levels of calcium and should not take calcium supplements.

People with a history of kidney stones should not take calcium supplements. However, some research suggests that calcium in the diet may not increase the risk of kidney stones. If you have or have had kidney stones, talk to your doctor about whether you should restrict calcium in your diet.

Men at risk for prostate cancer should avoid calcium supplements and also talk to their doctor about restricting low-fat dairy in their diets. Several studies have shown that higher intakes of calcium, whether from supplements or dairy products, are associated with greater risk of prostate cancer.

If you are currently being treated with any of the following medications, you should not use calcium supplements without first talking to your doctor.

Alendronate -- Calcium may interfere with the absorption of alendronate, a medication used to treat osteoporosis. Calcium-containing products should be taken at least 2 hours before or after alendronate.

Antacids that contain aluminum -- When calcium citrate is taken with aluminum-containing antacids, the amount of aluminum absorbed into the blood may be increased significantly. This is a particular problem for people with kidney disease, for whom the aluminum levels may become toxic.

Blood pressure medications -- Taking calcium with a beta-blocker (such as atenolol) may interfere with blood levels of both the calcium and the beta-blocker. Study results are conflicting, however. Similarly, it has been reported that calcium interferes with calcium channel blockers (such as verapamil), but these study results are also controversial. If you take a beta-blocker or calcium-channel blocker, do not take calcium supplements without your doctor’s supervision.

Cholesterol-lowering medications -- A class of medications known as bile acid sequestrants (including cholestyramine, colestipol, and colesevelam), used to treat high cholesterol, may interfere with normal calcium absorption and increase the loss of calcium in the urine. Supplementation, therefore, with calcium and vitamin D may be recommended by your health care provider.

Corticosteroids -- If you take corticosteroids on a long-term basis, you may need to take calcium supplements.

Digoxin -- High levels of calcium may increase the risk of a toxic reaction to digoxin, a medication used to treat irregular heart rhythms. On the other hand, low levels of calcium cause digoxin to be ineffective. If you take digoxin, your doctor should monitor your calcium levels closely.

Diuretics -- Different types of diuretics interact with calcium in opposite ways.

• Thiazide diuretics (such as hydrochlorothiazide) can raise calcium levels in the blood.
• Loop diuretics (such as furosemide and bumetanide) can decrease calcium levels.
• Amiloride (a potassium-sparing diuretic) may decrease the amount of calcium excreted in the urine (thus increasing calcium levels in the blood), especially in people with kidney stones.

Estrogens -- Estrogens may contribute to an overall increase in calcium blood levels. Taking calcium supplements with estrogens improves bone density significantly.

Gentamicin -- Taking calcium during treatment with the antibiotic gentamicin may increase the potential for toxic effects on the kidneys.

Antibiotics -- Different types of antibiotics interact with calcium.

• Quinolones: Calcium can interfere with the body's ability to absorb quinolone antibiotics (such as ciprofloxacin or Cipro; levofloxacin, norfloxacin or Noroxin; and ofloxacin). Take calcium supplements 2 - 4 hours before or after taking quinolone antibiotics
• Tetracyclines: Calcium can interfere with the body's ability to absorb tetracycline antibiotics (including doxycycline, minocycline, and tetracycline). Take calcium supplements 2 -4 hours before or after taking quinolone antibiotics.

Anti-seizure medications -- Some seizure medications, such as phenytoin (Dilantin), carbamazepine, phenobarbitol, and primidone, may lower levels of calcium in the body. Some doctors recommend vitamin D along with anti-seizure drugs to try to keep calcium levels up. In addition, you should take doses of calcium and anti-seizure medications at least 2 hours apart, because each interferes with the absorption of the other.

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