Preventing osteoporosis.

Not long ago I heard a doctor on television say, "Astronauts, bedridden hospital patients, and people who do not get enough exercise are all highly susceptible to a disease called osteoporosis." I thought this was rather strange. After all, astronauts are well-conditioned people; how could they develop osteoporosis? However, the doctor had aroused my curiosity, and I began to search for some answers.

Osteoporosis, the brittle bone disease, is a common disorder that affects slightly over 15 percent of the population. Although both men and women develop osteoporosis, it occurs more frequently in women. The disease results from the gradual loss of calcium and other minerals from the bones, making a person more susceptible to broken bones, joint injury, and poor posture. Certain lifestyle and dietary practices, such as eating a diet rich in calcium, avoiding excessive protein, and getting plenty of exercise, can help prevent osteoporosis.

Too little calcium. Some people don't like the taste of milk or are unable to tolerate it. Although milk is an excellent source of calcium, there are alternatives to drinking milk to get enough calcium. Foods such as pizza, macaroni and cheese, pudding, and vegetarian lasagna are all sources of calcium. Other foods such as yogurt, tofu, oranges, and wholewheat bread also contain calcium.

Some people add calcium to their diet through supplements. If you choose to take them, avoid taking an iron supplement at the same time since the iron supplement will decrease the body's ability to absorb the calcium.

Allowance (RDA) for calcium is 800 milligrams per day for men and women over 25 years of age, but 1,200 milligrams per day for both males and females 11 to 24 years of age. Young men seem to take in an appropriate amount of calcium, but young women seldom do. The average intake in young females is less than 600 milligrams per day. There is growing concern that young women may not consume enough calcium to make bones strong enough to last throughout their lifetime.

Eating too much protein. High protein diets contribute to flushing calcium out of the body through the urine; therefore, no more than 12 to 15 percent of your day's calories should come from protein sources (e.g., eggs, milk, cheese). In addition, an ex- cess intake of phosphorous (found in soft drinks and red meats) can accelerate bone mineral loss (osteoporosis). Phosphorous intake should be examined and reduced, if necessary. A registered dietician or health professional can assist you with doing this. Not enough exercise. Wolf s law tells us that exercise and nontraumatic stress enhance both the size and strength of bones. The weightlessness of space and the inactivity associated with being bedridden do not stress the skeletal system enough. This in turn increases the rate of calcium loss, which is why astronauts and bedridden patients are susceptible to osteoporosis. An active lifestyle that involves moderate activity (such as using the stairs rather than the elevator) and/or modest amounts of exercise can help increase the mineral content of the bones in the body. Even older women have increased their bone mineral content with weight-beating exercise together with adequate calcium intake. These simple tips can help you develop and maintain strong healthy bones.

Bradley J. Cardinal, Ph.D., is assistant professor of health at Wayne State University, Detroit, Michigan.