Calcium

Renowned for preventing -- or at least minimizing -- the devastating effects of osteoporosis, calcium is now thought to lower high blood pressure and prevent colon cancer. Unfortunately, this important mineral is often seriously lacking in the modern American diet.

Common Uses Maintains bones and teeth. Helps prevent progressive bone loss and osteoporosis. Aids heart and muscle contraction, nerve impulses, and blood clotting. May help lower blood pressure in people with hypertension. Eases heartburn.
Forms Tablet Capsule Softgel Powder Liquid
Warnings People who have thyroid or kidney disease should check with their doctor before taking calcium. Calcium may decrease the absorption of some antibiotics such as doxycycline, minocycline, and tetracycline. It may intensify the potassium-depleting effects of diuretics such as chlorothiazide, hydrocholorothiazide, and indapamide. Avoid calcium supplements made from dolomite, oyster shells, or bonemeal because these compounds may contain unacceptable levels of lead. Reminder: If you have a medical condition, talk to your doctor before taking supplements.
What It Is Although it's the most abundant mineral in the body, most adults get just half the calcium they need each day. Eating enough calcium-rich foods may be difficult, but you can prevent a deficiency by taking supplements. A wide array of products line store shelves. The most common forms are calcium carbonate, calcium citrate, calcium citrate malate, calcium gluconate, calcium phosphate, and calcium lactate. A supplement's elemental (or pure) calcium depends on its accompanying compound. Calcium carbonate (useful in antacids to relieve heartburn) provides 40% elemental calcium, while calcium gluconate supplies 9%. The lower the calcium content, the more pills you need to meet recommended amounts.

What It Does

The majority of the body's calcium is stored in the bones and teeth, where it provides strength and structure. The small amount circulating in the bloodstream helps move nutrients across cell membranes and plays a role in producing the hormones and enzymes that regulate digestion and metabolism. Calcium is also needed for normal communication among nerve cells, for blood clotting, for wound healing, and for muscle contraction. To have enough of this mineral available in the blood to perform vital functions, the body will steal it from the bones. Over time, too many calcium withdrawals leave bones porous and fragile. Only an adequate daily calcium intake will maintain healthy levels in the blood -- and provide enough extra for the bones to absorb as a reserve.

Prevention: Getting enough calcium throughout life is a central factor in preventing osteoporosis, the bone-thinning disease that leads to a higher risk of hip and vertebrae fractures, spinal deformities, and loss of height. The body is best equipped to absorb calcium and build up bone mass before age 35, but it's never too late to increase your intake of it. Several studies show that even in people over age 65, taking calcium supplements and eating calcium-rich foods help maintain bone density and reduce the risk of fractures.

Additional benefits: By limiting the irritating effects of bile acids in the colon, calcium may reduce the incidence of colon cancer. Other research indicates that diets that include plenty of calcium—as well as fruits and vegetables—may actually help lower blood pressure as much as some prescription medications do.

How much you need: The National Academy of Sciences, which sets the Recommended Dietary Allowances (RDAs), has recently increased its recommendations for daily calcium intake to 1,000 mg for men and women ages 19 to 50, and to 1,200 mg for those ages 50 to 70.

If you get too little: A prolonged calcium deficiency can lead to bone abnormalities, such as osteoporosis. Muscle spasms can result from low levels of calcium in the blood.

If you get too much: A daily calcium intake as high as 2,500 mg from a combination of food and supplements appears to be safe. However, taking calcium supplements may impair the body's absorption of the minerals zinc, iron, and magnesium. And very high doses of calcium from supplements might lead to kidney stones. Calcium carbonate may cause gas or constipation; if this is a problem, switch to calcium citrate.

Shopping Hints If you are over age 65, purchase calcium citrate. People over this age often lack sufficient stomach acid to absorb calcium carbonate.
How to Take It

Dosage: Be sure to get the recommended amount of 1,000 to 1,200 mg of elemental calcium a day from foods, supplements, or both. It's often a good idea to also add supplemental magnesium when taking calcium.

Guidelines for use: To enhance absorption, divide your supplement dose so that you don't consume more than 600 mg of calcium at any one time, and be sure to take the supplements with food.

Calcium cannot be absorbed without vitamin D, which is made by the skin in response to sunlight. Because your body's ability to convert sunlight to vitamin D declines with age, your safest bet is to get 200 to 400 IU of vitamin D a day in your diet (fortified milk is the best source) or in supplement form. You can also buy calcium supplements with vitamin D.

Other sources: The most familiar and plentiful sources of calcium are dairy products, such as milk, yogurt, or cheese. Choose low- or nonfat varieties: They're better for you and also contain slightly more calcium, ounce for ounce. Orange juice fortified with calcium malate, canned salmon and sardines (eaten with the soft bones), collard greens, arugula, broccoli, and almonds are good nondairy sources (but you'd have to eat nearly 80 florets of broccoli to get the 1,200 mg of calcium recommended daily). Spinach, however, is not a good source of calcium. It contains high levels of substances called oxalates, which lock up the calcium and limit the amount available to the body. The oxalates don't interfere with calcium absorption from other foods eaten at the same time, however.