Minimizing the loss of bone density


March 15, 1994|By Dr. Genevieve Matanoski | Dr. Genevieve Matanoski,Medical Tribune News Service

As a society, we have become more conscious of the need to build and keep bones healthy. Osteoporosis, or loss of bone density, has become a major medical concern as the population of the United States ages. Women are particularly vulnerable, since menopause causes additional loss of calcium in the bones, which makes them more brittle.

Advertisers now tout the addition of calcium to orange juice and even antacid tablets. But there is more to the battle against osteoporosis than just conspicuous consumption of calcium, and women need to learn all they can to avoid this common disability.

Q: What is osteoporosis?

A: Osteoporosis is the medical term for the reduction in bone density. This reduction occurs with increasing age, with menopause in women and with prolonged bed rest. It also becomes more pronounced with lack of exercise.

As women's bones become thinner, they are more vulnerable to fracture. So much so that even the usual traumas of daily living can cause the collapse of a vertebra in the spine.

Of course, the great fear for elderly women is always that of hip fractures. For the elderly, the risk of hip fractures increases 10 times, from about 0.2 percent per year at age 65 to 2 percent at age 80. Such fractures often result in prolonged disability and unwanted stays in either hospitals or nursing homes.

Q: How does osteoporosis occur?

A: Osteoporosis is the result of a loss of calcium in the body. Because calcium is essential for many processes in the body, we build a storehouse of calcium in our bones that our bodies can call on any time our intake is low.

If we have adhered to a diet high in calcium and with sufficient vitamin D, and simultaneously exercised for both strength and cardiovascular fitness, we approach menopause with high calcium reserves and high bone density. That, of course, is an optimal situation.

When menopause begins, and our estrogen supplies decrease, our bones begin to lose their calcium stores and become thin. There is an initial early rapid loss which begins to slow about five years after menopause. After that, we are left with a loss due to aging of about 1 percent per year.

The loss of calcium appears first in the central or trabecular bone. This leads to vertebral fractures, which then produce the typical shortening and bending of the spine that can cause the hump and reduced height that is common in older women.

Later loss of bone occurs at the outer edge or cortical bone. This leads to arm-bone fracture with falls.

Q: What role does estrogen replacement therapy (ERT) play?

A: If estrogen is taken during menopause, then the short-term rapid bone loss of 2 percent a year can be avoided. However, estrogen must be taken continuously because the rapid bone loss will begin whenever the therapy is withdrawn.

This is why scientists think that there are two forms of bone loss -- one that results from estrogen withdrawal and one that results from aging. Most estimates place the loss from estrogen at about 10 to 15 percent. So, if women have lifelong estrogen therapy, their bone density will be decreased by 10 percent at age 80 compared with 30 percent without ERT.

Q: Will taking calcium supplements change bone density after menopause?

A: Although all women have bone loss with increasing age, those with high calcium intakes have a reduced loss, according to most scientists.

To achieve a slower bone loss, most elderly must add calcium supplements. This may be due to a number of causes, such as low exposure to sunlight, decreased efficiency of the skin in making vitamin D products necessary for calcium absorption, and low intake of milk, which is a dietary source of vitamin D.

Although calcium supplements for the elderly appear to be the logical solution, this tactic also has drawbacks. For one thing, calcium tablets can cause stomach discomfort. Plus, women would need to take huge amounts to make a difference.

Second, the older we get, the more we would need. Finally, supplements differ in the amount of calcium that is available for absorption. The brands that are most readily available and which are least expensive are formed from calcium carbonate, a product of shells. This is a hard form to absorb. Calcium citrate is the preferred source of calcium since it is more readily absorbed, and you do not have to consume as much to get the same effect.

Dr. Genevieve Matanoski is a physician and epidemiologist at the Johns Hopkins School of Hygiene and Public Health. She is a founding director of the school's Institute for Women's Health Research and Policy.

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