Author: Simon Kipersztok, M.D., University of Florida

Prevention of Post-Menopausal Osteoporosis

An understanding of the biology of bone acquisition and bone loss throughout life can allow practitioners to utilize strategies useful in the prevention of osteoporosis. Peak bone mass is achieved between the third and fourth decades of life. This amount of bone is important since after its acquisition there is a natural decline in bone mass that is more prominent in women than in men. The higher the peak bone mass achieved, the lower the likelihood that later in life a given individual will experience an increased probability of fracture. There are many factors that can affect the acquisition of peak bone mass and they include: nutrition, level of exercise, the effect of some medical conditions, habits such as smoking, alcohol intake and genetic make up. For women a uniquely important factor is the amount of circulating estrogens beyond puberty.

Nutrition plays an important role in the acquisition of bone mass at many levels and for this reason, comprehensive nutritional counseling is important in the prevention of osteoporosis particularly for children, adolescents and young adults who are on their way to acquire peak bone mass. The two main nutritional components that should be addressed as part of a complete nutritional counseling program are calcium and vitamin D.

Calcium is an essential component of many biochemical processes and bone serves as a reservoir for the mineral. Parathyroid hormone maintains calcium homeostasis at the expense of bone integrity. In children and adolescents BMD is increased after calcium supplementation and in post-menopausal women calcium is important in maintaining adequate BMD although by itself it cannot prevent bone loss. A consensus panel from the National Institutes of Health has published guidelines for adequate calcium intake at different ages [8]. Several calcium supplements are commercially available however absorption from the supplements is not complete and some supplements can cause side effects such as bloating and constipation. Several commonly ingested foods have relatively high calcium content (see Table 3) [9].

Vitamin D plays an important role in calcium absorption and bone metabolism. The active metabolite can be synthesized in the skin under the influence of sunlight and therefore adequate daily supplementation is required in doses of 400-800 IU in individuals who are institutionalized or live in geographical areas where there is inadequate sun exposure. The supplementation may also be necessary for healthy postmenopausal women. A recent study showed that multivitamin therapy corrected low serum levels of vitamin D in healthy postmenopausal women living around the Atlanta, Georgia area where winters are relatively milder than in the Northern states [10]. Milk is an excellent source of calcium and is usually fortified with vitamin D. However, a study found that vitamin D levels in commercially available milk bottles are not uniform and can vary widely [11].

Weight bearing exercise is also necessary for competent bone mass since individuals with sedentary lifestyles can have lower BMD than individuals who exercise regularly. In this regard two issues are important to women. The first one has to do with premenopausal women who exercise to a degree where menstrual function is lost due to down regulation of the hypothalamus and pituitary. Some of these individuals develop exercise induced amenorrhea. Relative or absolute hypoestrogenism in this group of women can cause accelerated bone loss to a degree similar to that seen in postmenopausal women. This can be treated by adjusting the exercise regimen in such a way that regular menstrual periods occur or by replacing estrogen with HRT or oral contraceptives. The second issue has to do with the potential for trauma that can occur at different anatomical sites in postmenopausal women who have low bone densities and engage in an exercise program. For those women a consultation with a physical therapist can be helpful.

Accurate diagnosis and treatment of several medical and psychiatric conditions that can adversely affect bone mass is an important preventive strategy. Excess thyroid hormone, either as a result of undiagnosed hyperthyroidism or as a consequence of poorly monitored replacement for patients with hypothyroidism, can cause bone loss. Similarly, glucocorticoid therapy for chronic rheumatologic, renal, pulmonary or allergic conditions can cause bone loss by a direct effect on bone and also by down regulating the hypothalamus and pituitary and causing hypoestrogenism. Some younger women can develop eating disorders such as anorexia nervosa and bulimia which in turn can lead to hypoestrogenism due to hypothalamic amenorrhea and cause subsequent bone loss. These eating disorders can be dangerous and on occasion lead to death. Psychiatric intervention is often required and during treatment patients can be replaced with HRT or oral contraceptives.

Smoking is associated with low BMD. Compared to nonsmokers, smoking women usually experience the menopause at an earlier age. This is possibly due to a direct toxic effect of tobacco or its by products on the ovary. Also, smoking women clear estrogens from their system more readily than non smoking women [12]. Similarly, individuals who drink heavily have lower BMD compared to non drinkers or moderate drinkers. This can be the result of a direct toxic effect of alcohol on bone metabolism or a result of the systemic effects that alcohol abuse has on heavy drinkers. Also, heavy drinkers not uncommonly suffer from nutritional deficiencies which in turn can have a deleterious effect on bone. When counseling patients about the adverse effects that smoking and excessive drinking have on their health it is important to highlight the detrimental influence that these agents can have on bone metabolism.

Whites and Asians have, on the average, lower bone masses than other ethnic groups and this observation is thought to be due to genetic differences. While targeting preventive strategies to ethnic groups at higher risk for the condition makes public health sense, it is important to remember that members of any ethnic group can still suffer from osteoporosis and its sequelae due to factors other than genetic.