16.4: Risk Factors

Looking at all the ads for calcium supplements, one would think that osteoporosis was simply caused by a deficiency of calcium in the diet. In fact, osteoporosis is a very complex disease brought about by an interplay of many factors (see Table 16-2). Some of these are:

• Gender: As said earlier, women are at higher risk. They have smaller bones, their bones are less dense at their peak, their rate of bone loss accelerates at menopause, and they live longer than men. Both the male hormone testosterone and the female hormone estrogen help preserve bone mass. Whereas there’s a rapid fall in estrogen for women at menopause, aging men have a small and gradual fall in testosterone. In addition, men’s estrogen levels increase with advancing age. (These hormonal changes in men may contribute to their “mellowing” as they age.)
• Family history: Having a close relative (e.g., parent, grandmother) with osteoporosis increases risk. Genes not only influence bone density but also bone size. Small-boned women have less bone to lose. (Also, of course, families share food and exercise habits.)
• Race: Osteoporosis is more common among whites, Asians, and Hispanics than among blacks, presumably because of racial differences in bone density. At comparable ages, blacks have higher bone density (even though their calcium intake is lower), and, as a result, black women have about half the number of hip fractures of white women. Women who have very light skin (e.g., those with naturally blond or red hair) have a higher risk.
• Physical activity: Normal physical activity preserves bone mass, whereas prolonged bed rest results in marked bone loss. The importance of stress on bone is most dramatically demonstrated by astronauts’ rapid bone loss during space travel, when they escape the pull of gravity.

The greatest effect of physical activity on bone mass occurs in the range of minimal to normal physical activity. In addition, moderate, stress-bearing exercise is helpful. As with muscles, the effects are very specific. Bone density is higher (and the muscles larger) in the playing arm of a tennis player than in the other arm.

Also, we sometimes need to be reminded that “getting exercise” doesn’t necessarily mean we have to take up a sport or “work out.” Such activities as vigorously scrubbing the bathroom or using a manual lawn mower also provide good exercise. A caveat: premenopausal women who engage in strenuous exercise to the point of amenorrhea (stoppage of menstruation) can lose bone mass. Amenorrhea has some of the same characteristics as menopause.

• Body weight: Osteoporosis is less common among those who are overweight, perhaps because carrying extra weight puts more stress on bones (and extra body fat provides more cushioning for the bone in a fall). Also, because fat cells make some estrogen, they become an important source when ovary-produced estrogen falls after menopause. Among premenopausal women, extreme thinness to the point of amenorrhea (many ballerinas and women with anorexia nervosa have this problem) can result in losses of bone mass.
• Smoking: Smoking appears to increase the risk of osteoporosis for both men and women. The reason isn’t entirely clear, but women who smoke tend to have an earlier onset of menopause (by about 5 years). This results in accelerated bone loss at an earlier age. Also, smokers tend to weigh less than non-smokers. As noted earlier, a heavier body weight and more fat tissue can offer some protection against osteoporosis.
• Alcohol: Osteoporosis is more common among alcoholics, presumably because they tend to have poor diets that are deficient in calcium and other nutrients, and because excessive alcohol can lessen the absorption of nutrients by damaging the intestinal lining. Also, excessive alcohol consumption increases the risk of falling, and consequently the risk of fractures.
• Dietary calcium: Dietary calcium does play a role in osteoporosis, but its role isn’t as large as ads for supplements would have you believe. It’s important, of course, to meet your dietary requirement. The ads and magazine articles encouraging calcium intake are mostly directed at women, but young girls should be the focus.

Beginning at about age 11, girls’ average intake of calcium falls below recommended levels—and persists for females at every age thereafter. Adequate calcium intake during childhood and young adulthood is crucial for obtaining a high peak bone mass. Of special concern are growing girls who are thin, small boned, sedentary, fair-skinned, continually dieting, and who consume very little milk or milk products.

• Other nutrients: Various other nutrients can potentially affect risk of osteoporosis, mainly through their effect on calcium absorption and losses. We saw in the previous chapter, the important role of Vitamin D. High amounts of sodium and protein can increase the loss of calcium in the urine, but its effect on the risk of osteoporosis hasn’t been established.

Prevention

As can be seen from the discussion of risk factors, the best that children, adolescents, and adults can do to prevent osteoporosis is to eat a good diet, get a moderate amount of stress-bearing exercise, and not smoke.

Preventive therapies to retard bone loss for post-menopausal women has included estrogen-replacement therapy at the start of menopause. Studies have shown that when estrogen therapy is begun at menopause, the number of hip and wrist fractures is about half that of comparable women who aren’t given estrogen. Not all women are suitable for this therapy, including those who are many years past menopause and have already lost a lot of bone, women who have had breast cancer, and women with certain health problems such as liver disease or very high blood pressure.

Figure 16-5: Peak bone density is a crucial factor in the risk of osteoporosis.

As with all medications, there’s concern about possible side-effects of estrogen-replacement therapy, a major concern being estrogen-related cancers. Estrogen used to be given alone, and this was found to increase the risk of cancer in the lining of the uterus (endometrial cancer). Now, estrogen is given together with another hormone (progestin) that greatly reduces—and possibly eliminates—the risk of this cancer.

In the Women’s Health Initiative study, more than 16,000 postmenopausal women ages 50-79 were randomized into estrogen-progestin and placebo groups. In the 5.2-year average follow-up, the estrogen-progestin group had fewer bone fractures and fewer colon and rectal cancers, but more breast cancer, heart disease, and stroke.¹

As a result of this study, many women on hormone replacement therapy stopped abruptly. Instead, many women are taking bisphosphonates (e.g., Fosamax) to prevent osteoporosis. Bisphosphonates retard bone loss.^2,3