Calcium is a mineral important for strong bones and teeth. It also helps your heart, nerves, muscles, and other body systems work properly. Milk and dairy products, such as cheese and yogurt, give you most of the calcium you get from food, but you can also get it from nuts, green leafy vegetables, and calcium-enhanced orange juice. Vitamins A, C, D, and E help you use the calcium you get from food. Stress and lack of exercise can harm your calcium balance. Most people in the United States, especially women, do not get enough calcium in their diet.

Getting enough calcium can help your body do the following:

• Develop strong bones and teeth
• Prevent osteoporosis and broken bones
• Reduce your blood pressure
• Lower your cholesterol levels
• Keep your heart regular
• Reduce cramps and moodiness from premenstrual syndrome
• Reduce irritability, insomnia, depression, and headaches during menopause
• Reduce risks of pregnancy, such as high blood pressure and preeclampsia
• Prevent gum disease
• Prevent cancer of the colon and rectum
• Prevent kidney stones

The richest sources of calcium include cheeses (Parmesan, Romano, Gruyère, Swiss, Provolone, Monterey Jack, Edam, Cheddar, Muenster, Gouda, Tilsit, Colby, Caraway, Brick, Roquefort, Port du Salut, Cheshire, Havarti, Fontina, Mozzarella, Feta); wheat-soy flour; blackstrap molasses; and rennin.

Other good sources of calcium include almonds, bok choy, Brazil nuts, broccoli, cabbage, caviar, dried figs, greens (dandelion, turnip, collard, mustard, kale), hazelnuts, ice cream, milk, oysters, sardines, soybean flour, and yogurt.

You can also get calcium from many herbs, spices, and seaweeds (for example, basil, chervil, cinnamon, dill weed, fennel, fenugreek, ginseng, kava kava, kelp, marjoram, oregano, parsley, poppy seed, sage, and savory).

Calcium is available in many forms. Lead has been found in some types, so use caution when choosing a product. Lead is a toxic metal that can harm the brain and kidneys, and can reduce red blood cell production. Children are most at risk for lead poisoning. The following are some of the available forms of calcium:

• Calcium citrate. This is the most easily used form of calcium, and the most easily digested. Lead levels are safe. It is especially recommended for elderly persons, people taking ulcer medication, and people who want to lower their blood pressure.
• Calcium carbonate. This type is less expensive, and lead levels are safe if it is refined. Rolaids and Tums contain calcium carbonate. Other antacids contain aluminum and can harm your calcium balance.
• Calcium gluconate. This type is safe.
• Calcium lactate. This is another safe form.
• Calcium chloride. This is not recommended because it irritates the gastrointestinal tract.

You should be cautious with products that may contain harmful levels of lead. These include unrefined calcium carbonate from oyster shells or limestone, bone meal, and Dolomite.

You should take small doses throughout the day, and drink 6 to 8 cups of water throughout the day to avoid constipation.

• Adults ages 19 to 50 need 1,000 mg of calcium each day. After age 50, adults need 1,200 mg each day.
• Adolescents ages 9 to 18 need 1,300 mg each day.
• Children ages 6 to 8 need 800 mg each day; children ages 1 to 5 need 500 mg each day.

Do not take extremely large doses of calcium (5,000 mg per day, or 2,000 mg per day or more over a long period) without talking with your health care provider. High doses can cause kidney stones and other serious problems.

Avoid calcium products that contain harmful levels of lead (see above).

Talk with your provider about your calcium needs if you have any thyroid or kidney problems, or if you have hormone or vitamin deficiencies.

Taking calcium during treatment with the antibiotic gentamicin may increase the potential for toxic effects on the kidneys; therefore, calcium should be used with caution, if at all, in people taking gentamicin. In addition, calcium can interfere with the body's ability to absorb quinolone antibiotics such as ciprofloxacin, as well as tetracyclines, and should not be taken at the same time as these antibiotics. Calcium may also interfere with the absorption of alendronate, a medication used to treat osteoporosis (bone loss). Products containing calcium should be administered at least two hours before or after both alendronate and tetracyclines. Some corticosteroid medications also reduce the absorption of calcium, thereby increasing the risk for osteoporosis over time. Please refer to the depletions monograph on corticosteroids for more information.

Two different classes of diuretics interact with calcium in opposite ways—thiazide diuretics such as hydrochlorothiazide can raise calcium levels in the blood, while loop diuretics such as furosemide and bumetanide can decrease calcium levels. In addition, amiloride, a potassium-sparing diuretic, may decrease the amount of calcium excreted in the urine, especially in people with kidney stones; this could raise the levels of calcium levels in the blood. Therefore, taking calcium supplements during treatment with amiloride or thiazide diuretics may not be appropriate or warranted. You should consult with your healthcare provider before adding calcium to your existing medication regimen. Please refer to the depletions monograph on loop diuretics for more information about the effects of reduced calcium levels from these medications.

High levels of calcium may increase the likelihood of a toxic reaction to digoxin, a medication used to treat heart conditions, including symptoms of arrhythmia (irregular heartbeat); however, low levels of calcium cause digoxin to be ineffective. People who are taking digoxin should have calcium blood levels monitored closely.

Taking calcium with atenolol, a beta-blocker used for the treatment of high blood pressure or heart disorders, may interfere either with blood levels of calcium or this medication; study results are conflicting. Until more is known, individuals taking atenolol should have their blood pressure checked before and after adding calcium antacids or supplements to their medication regimen. Similarly, it has been reported that calcium may reverse the therapeutic effects as well as the side effects of verapamil, a calcium channel blocker often prescribed for the treatment of high blood pressure; there are conflicting reports regarding these results. Again, blood pressure should be monitored closely in patients taking calcium while being treated with verapamil. Consult with your healthcare provider before adding calcium if you are currently taking atenolol or verapamil.

While conjugated estrogens may contribute to an overall increase in calcium blood levels, taking calcium supplements may still be advisable in postmenopausal women on hormone replacement therapy to protect against the risk of developing osteoporosis. For women 51 years or older, the dietary reference intake (DRI) for calcium is 1200 mg/day.

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