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Bone is a living tissue which is always changing. New bone is constantly being made and old bone is constantly being taken up or reabsorbed. These two processes are coupled together and normally balance each other out so that there is no net bone loss.

Osteoporosis occurs when this balance is altered and the bone thins out, although the mineral content remains the same. This means that osteoporotic bone is much more susceptible to fractures, especially of the vertebrae in the spine, the wrist bone and the hip bone.

Osteoporosis is an enormous and very costly health problem. In the U.S. approximately 25 million people are affected and one million people develop osteoporosis-related fractures every year. By age 70, over 40 percent of women have evidence of at least one fracture. By age 90, more than a third of women suffer hip fractures.

In the U.S., the latest estimate for the cost of treating fractures caused by osteoporosis is ten billion dollars per year.

In Canada, 800,000 Canadians are now suffering from fractures and another 2.5 million are seriously at risk for these osteoporosis-related fractures.

As Dr. Robert Josse, Chief of Endocrinology and Metabolism at Saint Michael's Hospital in Toronto told a symposium in Ottawa:

"Something in the order of 25 percent of post-menopausal Caucasian [white] North American women have this disease. More than 20 percent of elderly patients may die within three months of a fracture, and 15 to 20 percent of individuals are institutionalized within one year of the event."

Dr. Josse estimates that the cost of treating all fractures associated with osteoporosis "would tally between $250 to $300 million for the year 1989."

Dr. Josse distinguishes between two types of osteoporosis. The first type affects mainly women between the ages of 51 and 70 and consists of loss of the spongy inner part of bone (called trabecular bone). Loss of this type of bone occurs most rapidly in the first five years after menopause. Weakening of this type of bone leads primarily to fractures of the spinal column and the wrist.

The second type of osteoporosis occurs in both men and women aged 70 or over, and consists of loss of both the trabecular bone as well as the hard outer part of the bone known as cortical bone. This commonly causes fractures of both the hip and the spinal column.

Osteoporosis is mainly a problem of the Western world. As Janine O'Leary Cobb notes in her excellent book, UNDERSTANDING MENOPAUSE (Key Porter, revised 1993).

"Osteoporosis is not a worldwide, female only problem. It is more common in affluent, northern countries. Women who have had multiple pregnancies, who eat red meat infrequently, who do strenuous physical labour, and who are overweight [by our standards] are not likely to develop osteoporosis. These are the characteristics of the majority of the women in the world." Moreover, black women rarely suffer from osteoporosis since their bones are genetically denser than those of white women. Orientals are, however, vulnerable, presumably because they tend to be small-boned and slim; because their genetic bone structure is not dense."

Preventing Osteoporosis

WEIGHT BEARING EXERCISE: A sedentary lifestyle can definitely contribute to the development of osteoporosis. Exercise should be begun as soon as possible, but certainly by age 30 to build up peak bone mass. However, hereditary and racial factors may be the most important determinants of peak bone mass.