Functions

Calcium's functions include:

• Builds bones, both in length and strength
• Helps bones remain strong by slowing the rate of bone loss with age
• Helps muscles contract
• Helps the heart beat
• Plays a role in normal nerve function, transfers nerve impulses
• Helps blood clot during bleeding
• Builds healthy teeth (in kids)

Recommended Intake

Calcium Deficiency

In childhood, not getting enough calcium may interfere with growth; a severe deficiency may keep children from reaching their potential adult height. Even a mild deficiency over a lifetime can affect bone density and bone loss, which increases the risk for osteoporosis.

If you don't consume enough calcium, your body will draw from the storage in your bones in order to supply enough calcium for its other functions: nerve transmission, muscle contraction, heartbeat, and blood clotting.

Symptoms of a calcium deficiency include:

• Inadequate mineralization of bone
• Intermittant muscle contractions
• Muscle pain
• Muscle spasms
• Numbness or tingling in the hands and feet
• Rickets in children
• Osteoporosis in adults

Calcium Toxicity

Unless doses exceed 2500 mg/day, adverse effects for adults are unlikely. Very large doses over a prolonged period of time may cause kidney stones and poor kidney function. Your body may not absorb other minerals, such as iron, magnesium, and zinc, properly. These problems could occur from consuming too much through a calcium supplement, not from milk or other calcium-rich foods. The tolerable upper intake level (UL) is set at 2500 mg daily from age one through adulthood.

Major Food Sources

Dairy foods—milk, yogurt, and some cheeses—are the best dietary sources of calcium. These foods are also rich in vitamin D, which helps the body absorb calcium.

Absorption of calcium from some other dietary sources is not as great as that from dairy foods. Specifically, dark green vegetables contain oxalates, and grains contain phytates, which can bind with calcium and decrease their absorption.

Read labels on tofu and fortified products to determine specific calcium levels of these foods.

Health Implications

Bone health and osteoporosis prevention

Calcium is essential to build and maintain strong bones at all stages of life. Bone growth begins at conception, and bones grow longer and wider until well into the 20s. After this type of growth is complete, bones gain in strength and density as they continue to build up to peak bone mass by about age 35. From this point on, as a natural part of the aging process, bones slowly lose mass. Calcium is essential to slow this natural loss and stave off the onset of osteoporosis—a disease in which bones become fragile and more likely to break.

If not prevented or if left untreated, osteoporosis can progress painlessly until a bone breaks. These broken bones occur typically in the hip, spine, and wrist. Even when a person has osteoporosis, though, proper calcium and vitamin D intake can help to delay further bone loss.

Other health problems

Consuming enough calcium can also help protect you from high blood pressure, heart disease, and possibly colon cancer. Calcium supplementation (1500 mg/day) during pregnancy can also significantly reduce the risk of eclampsia, a severe seizure and blood pressure disorder that can be life threatening to both mother and baby.*

The relationship of calcium intake to kidney stones is complicated and variable between persons. Lowering calcium intake may not reduce the risk of kidney stones because the end result may be a lesser amount of calcium absorption, but a greater tendency for the calcium that is in the urine to form stones.

Many people do increase their risk of kidney stones by consuming excess calcium—usually in supplements. This risk can probably be decreased by taking calcium supplements with meals and perhaps by limiting intake of salt (sodium). When your diet contains more sodium daily than the currently recommended 2300 grams (about 1 teaspoon of table salt), then the kidneys respond by excreting more calcium into the urine. Not only does this lead to greater calcium loss (and risk of osteoporosis), but it exposes the kidneys to a greater risk of stone formation.

Dealing with lactose intolerance

Some people have difficulty digesting lactose, the main sugar in milk and some dairy products. This occurs when the body does not produce enough of the enzyme lactase to properly digest lactose. People with this condition, called lactose intolerance, may experience nausea, cramping, bloating, abdominal pain, gas, and diarrhea anywhere from 15 minutes to several hours after eating milk or milk products.

People with lactose intolerance can take the following steps to be sure they meet their calcium needs:

• Eat dairy foods along with a meal rather than alone; the presence of other foods in the digestive tract can make it easier for your body to tolerate the lactose.
• Eat smaller portions of dairy foods. Most people find that they are able to tolerate 1/2 cup or 3/4 cup of milk at a time, several times during the day, rather than 1 cup or more in one sitting.
• Choose aged cheeses, such as Swiss, Colby, Parmesan, and cheddar, which have most of their lactose removed during processing.
• Try dairy foods made with live, active cultures, such as yogurt and buttermilk. The "friendly" bacteria in these foods help to digest the lactose. These foods should have a "Live and Active Cultures" label.
• Be sure to include non-dairy sources of calcium in your daily diet.
• Consider the addition of a lactase enzyme supplement, such as Lactaid (or a generic product). For many people, taking an enzyme supplement can increase the amount of lactose that can be tolerated.

Tips for increasing your calcium intake

• When making oatmeal or other hot cereal, use milk instead of water.
• Add powdered milk to hot cereal, casseroles, baked goods, and other hot dishes.
• Make your own salad dressing by combining low-fat plain yogurt with herbs.
• Add tofu (processed with calcium) to soups and pasta sauce.
• If you like fish, eat canned fish with bones on crackers or bread.
• For dessert, try low-fat frozen yogurt, ice cream, or pudding.
• In baked goods, replace half of the fat with plain yogurt.

Taking supplements

If you are unable to meet your calcium needs through dietary sources, consider a calcium supplement. Some points to remember when choosing and using a calcium supplement include:

• Check the label because the amount of calcium differs among products.
• Avoid supplements with dolomite or bone meal; they may contain lead.
• Check your vitamin D intake, too. This vitamin is essential for absorption of calcium. Milk is a great source of vitamin D, as is sunlight.
• Ask your doctor if you should take a supplement.
• If you take both calcium and iron supplements, take them at different times of the day. They can impair each other's absorption
• If you take more than 500 mg of supplemental calcium, space it out throughout the day; it's better absorbed that way. It's also best absorbed with food, so take one tablet with breakfast and another with dinner.

References:

The Nutrition Desk Reference. Keats Publishing; 1995.

Food and Nutrition Information Center. US Department of Agriculture website. Available at: http://fnic.nal.usda.gov/nal_display/index.php?tax_level=1&info_center=4.

Advanced Nutrition and Human Metabolism. West Publishing Company; 1995.

Bowes & Church Food Values of Portions Commonly Used. Lippincott Williams & Wilkins; 1998.

Domrongkitchaiporn S, Sopassathit W, Stitchantrakul W, Prapaipanich S, Ingsathit A, Rajatanavin R. Schedule of taking calcium supplement and the risk of nephrolithiasis. Kidney Int. May 2004 ;65(5):1835-1841.

Hofmeyr GJ, Atallah AN, Duley L. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database Syst Rev. Jul 19, 2006;3:CD001059.

Villar J, Abdel-Aleem H, Merialdi M, et al. World Health Organization randomized trial of calcium supplementation among low calcium intake pregnant women. Am J Obstet Gynecol. Mar 2006;194(3):639-649.

*Updated section on Functions on 7/6/06 according to the following study, as cited by DynaMed's Systematic Literature Surveillance: Villar J, Abdel-Aleem H, Merialdi M, et al. World Health Organization randomized trial of calcium supplementation among low calcium intake pregnant women. Am J Obstet Gynecol. Mar 2006;194(3):639-649.

ThirdAge WWW