Calcium is the most abundant mineral in your body. It is essential for the development and maintenance of strong bones and teeth, where about 99% of the body's calcium is found. Calcium also helps the heart, nerves, muscles, and other body systems work properly. It is probably best known for helping prevent 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. Many factors, including age, disease states, and medications, can affect calcium absorption. Carbohydrates may enhance calcium absorption while coffee and cigarette smoke may impede it.

The best way to get calcium is through food. Many foods are fortified with calcium. But some people may need to take calcium supplements to get the recommended amount. It is especially important for children to get enough calcium in their diets as they are growing and forming bone, and for older people as they start to lose bone.

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 who don't absorb enough calcium, as can happen with Crohn's disease, celiac disease, and some intestinal surgeries.

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

Osteoporosis

Your body needs calcium to build and maintain healthy bones and strong teeth. People start to lose more bone than their bodies make in their 30s, and the process speeds up as they get older. Studies have shown that calcium, particularly in combination with vitamin D, may help prevent bone loss associated with menopause. It may also help prevent bone loss in older men. If you do not get enough calcium in your diet, your doctor may recommend a supplement.

Hypoparathyroidism

People with this condition have underactive parathyroid glands. These four small glands 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 doctors. 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 or high blood pressure. Some studies suggest that increasing calcium levels may lower blood pressure slightly. However, not all studies have been positive. 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. Instead, talk to your doctor about the right amount of calcium for you. You may need to take calcium for 6 to 8 weeks before you see any improvement in blood pressure.

Some studies suggest that calcium supplements may play a role in the prevention of high blood pressure during pregnancy and preeclampsia, a combination of high blood pressure, fluid retention, and high levels of protein in the urine that some women develop during the last trimester of pregnancy. However, not all studies show the same benefit. Taking a prenatal vitamin, with magnesium, folic acid, and many other nutrients, and getting enough calcium in food, may lower the risk of developing high blood pressure during pregnancy.

Obesity and Weight Loss

Animal and human studies have found that eating low-fat dairy products may help you lose weight or stay at a healthy weight. However, researchers aren't sure whether the calcium in the dairy products affects weight, or whether it's some other nutrient -- or even a combination of nutrients. In addition, not all studies have been positive. Plus there's no sound evidence that taking calcium supplements, as opposed to eating low-fat dairy products, would help with weight loss. 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 lower cholesterol slightly. From these studies, it seems that calcium supplements, along with exercise and a healthy diet, may be better at keeping cholesterol at normal levels than at lowering already high cholesterol. More research is needed.

Rickets

Rickets causes softening and weakening of the bone in children. Although very rare in North America and Western Europe, where children drink a lot of milk, it still happens in many parts of the world. Researchers thought rickets was caused by a vitamin D deficiency. But studies suggest that taking calcium supplements is an effective treatment.

Other Uses

Stroke. In a population-based study, in which large groups of people were followed over time, women who took in more calcium, both through food and 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 have higher amounts of calcium, vitamin D, and milk in their diets are less likely to develop colorectal cancer than those who have low amounts. Researchers are not sure whether calcium supplements would have the same effect, or even whether calcium itself is making the difference.

The richest food sources of calcium include:

• Cheeses, such as Parmesan, Romano, gruyere, cheddar, American, mozzarella, and feta
• Low-fat dairy products, such as milk and yogurt
• Tofu
• Blackstrap molasses

Other good sources of calcium include:

• Almonds
• Brewer's yeast
• Bok choy
• Brazil nuts
• Broccoli
• Cabbage
• Dried figs
• Kelp
• Dark leafy greens (such as dandelion, turnip, collard, mustard, kale, and Swiss chard)
• Hazelnuts
• Oysters
• Sardines
• 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 many forms of calcium available as dietary supplements. They differ in the amount of calcium they contain, how well the body absorbs them, 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. It does not contain as much elemental calcium -- the amount your body actually absorbs -- as calcium carbonate. It is more expensive than calcium carbonate. Also, calcium citrate should not be used with aluminum-containing antacids.
• 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.

Avoid calcium supplements that are derived from oyster shells, dolomite, and bone meal as they may contain lead, a toxic metal 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) during the day with 6 to 8 cups of water to avoid constipation.

The following are daily dietary recommendations from the Institute of Medicine.

Pediatric

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

• Birth to 6 months: 200 mg
• 7 months to 1 year: 260 mg
• 1 to 3 years: 700 mg
• 4 to 8 years: 1000 mg
• 9 to 18 years: 1,300 mg

Adult

• 19 to 50 years: 1,000 mg
• Women 51 years and older: 1,200 mg
• Men 51 to 70 years: 1,000 mg
• Men older than 70: 1,200 mg
• Pregnant and breastfeeding women under 19 years: 1,300 mg
• Pregnant and breastfeeding women 19 years and older: 1,000 mg

For prevention of colon cancer, some researchers recommend 1,800 mg per day. Speak with your doctor to determine the right dose for you.

Take dietary supplements only under the supervision of a knowledgeable health care provider since there is a potential for side effects. 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 and vomiting
• Loss of appetite
• Increased urination
• Kidney damage
• Confusion
• Irregular heart rhythm

People with hyperparathyroidism, kidney failure, sarcoidosis, or cancer could be at risk for high 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 foods may not increase the risk of kidney stones. If you have or have had kidney stones, talk to your doctor about whether you should limit calcium in your diet.

Some population studies suggest that getting high amounts (more than 2,000 mg per day) of calcium through the diet may increase the risk of prostate cancer. Two of these studies found that low-fat and nonfat milk -- but not other dairy foods -- was associated with a higher risk of advanced prostate cancer. But these studies don't prove that drinking low-fat or nonfat milk causes an increased risk of prostate cancer. And some research suggests that the amount of calcium in the diet isn't associated with prostate cancer risk. If you have prostate cancer, or are concerned about dairy products and prostate cancer risk, talk to your doctor.

The Institute of Medicine sets the tolerable upper level of daily calcium intake at 2,500 mg. Some studies have suggested that getting amounts higher than 1,000 to 1,200 mg/day may be associated with an increased risk of heart attack. More research is needed.

When figuring out how much calcium you need, be sure to take into account the calcium-rich foods you eat -- such as cheese, yogurt, milk -- along with any supplements.

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

Ceftriaxone (Rocephin)

These medications may have potentially fatal interactions with calcium.

Biphosphates

These medications are used to treat osteoporosis and some other bone conditions. Calcium may interfere with how your body absorbs them. Calcium-containing products should be taken at least 2 hours before or after bisphosphonates. Bisphosphonates include:

• Alendronate (Fosamax)
• Etidronate (Didronel)
• Ibandronate (Boniva)
• Risedronate (Actonel)
• Tiludronate (Skelid)
• Zoledronic acid (Reclast)

Antacids that contain aluminum

When calcium citrate is taken with these antacids, the amount of aluminum absorbed into the blood may go up. For people with kidney disease, the aluminum levels could be toxic.

Blood pressure medications

Taking calcium with a beta-blocker may interfere with blood levels of both the calcium and the beta-blocker. Study results aren't clear, however. It also has been reported that calcium interferes with calcium channel blockers. But these study results are also mixed. If you take a beta-blocker or calcium-channel blocker, do not take calcium supplements without your doctor's supervision. Beta-blockers include atenolol (Tenormin), metoprolol (Lopressor, Toprol-XL), and propranolol (Inderal, Inderal LA), among others. Calcium-channel blockers include amlodipine (Norvasc), diltiazem (Cardizem), and nifedipine (Procardia).

Cholesterol-lowering medications

A type of medication known as bile acid sequestrants, used to treat high cholesterol, may interfere with calcium absorption and raise the amount of calcium that leaves the body in urine. Your doctor may recommend taking calcium and vitamin D supplements. These drugs include cholestyramine (Questran), colestipol (Colestid), colesevelam (Welchol).

Calcipotriene (Dovenex)

Taking calcium supplements while using calcipotriene, a topical medication for psoriasis, could increase the risk of having calcium levels that are too high (hypercalcemia).

Corticosteroids (prednisone)

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

Digoxin

High levels of calcium may raise the risk of a toxic reaction to digoxin, a medication used to treat irregular heart rhythms. On the other hand, low levels of calcium keep digoxin from working. If you take digoxin, your doctor should monitor your calcium levels closely.

Diuretics (water pills)

Different types of diuretics interact with calcium in opposite ways:

• Thiazide diuretics can raise calcium levels in the blood. These drugs include chlorothiazide (Diuril), hydrochlorothiazide, ghlorthalidone (Hygroton), indapamide (Lozol), metolozone (Zaroxolyn), and polythiazide (Renese), among others.
• Loop diuretics can decrease calcium levels. These drugs include furosemide (Lasix) and bumetanide (Bumex).
• Amiloride (Midamor) is a type of diuretic called a potassium-sparing diuretic. It may reduce the amount of calcium your body eliminates in urine, and raise 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.

Gentamicin

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

Sotalol (Betapace)

Sotalol is used to treat an irregular heartbeat. Calcium may decrease how much sotalol is absorbed by the body.

Thyroid hormone

Calcium can decrease the amount of thyroid hormone medication that your body absorbs.

Antibiotics

Different types of antibiotics interact with calcium:

• Quinolones. Calcium can interfere with the body's ability to absorb quinolone antibiotics. These drugs include ciprofloxacin (Cipro), levofloxacin (Levaquin), norfloxacin (Noroxin), and ofloxacin (Floxin). Take calcium supplements 2 to 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 to 4 hours before or after taking tetracycline antibiotics.

Anti seizure medications

Some seizure medications, such as phenytoin (Dilantin), carbamazepine (Tegretol), phenobarbitol, and primidone (Mysoline), may lower levels of calcium in the body. Some doctors recommend taking vitamin D along with anti seizure drugs to keep calcium levels up. 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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