Osteoporosis

Maintaining a healthy lifestyle might retard one detrimental aging process that is a major health concern for women: osteoporosis. Osteoporosis is characterized by decreased bone porosity. Osteopenia refers to a loss of bone mass that occurs with aging. Osteoporosis is a more severe loss of bone mass with deterioratioin of the microarchitecture of bone, leading to skeletal fragility and increased risk of bone fracture. These changes typically begin in the early 30s. The occurrence rate for fractures associated with osteoporosis increases by two to five times after the onset of menopause. Men also experience osteoporosis but to a lesser degree early in life because of a slower rate of bone mineral loss. Much remains to be learned about the etiology of osteoporosis; however, three major contributing factors common to postmenopausal women are:

• Estrogen deficiency,
• Inadequate calcium intake,
• Inadequate physical activity.

Although the first of these is a direct result of menopause, the last two reflect dietary and exercise patterns throughout life.

In addition to postmenopausal women, women with amenorrhea and those with anorexia nervosa also suffer from osteoporosis attributable to insufficient calcium intake, low serum estrogen levels, or possibly both. In studies of women with anorexia, investigators found that their bone densities were reduced significantly compared with those of controls. Cann and associates were the first to report a substantially lower than normal bone mineral content in physically active women classified as having hypothalamic amenorrhea.

In another study, the radial and vertebral bone densities of 14 athletic women(mostly runners) with amenorrhea were compared with those of 14 athletic women with normal menstruation(eumenorrhea). Investigators discovered that physical activity did not protect the group with amenorrhea from significant bone density losses. The amenorrheic group’s bone density values at a mean age of 24.9 were equivalent to those of normally active women at a mean age of 51.2. In a follow-up study, increases in vertebral bone mineral density were found in the women who previously had been amenorrheic but had resumed menstruation. However, their bone mineral densities remained well below the average for their age-group, even four years after they resumed normal menses.

It generally is assumed that exercise is a positive factor for bone health in that it is associated with an increase in bone mass, or at least with the maintenance of bone mass in young, middle-aged, and older women. Therefore, it is confusing to learn that amenorrheic runners have reduced bone mass. Bone mineral content of normally menstruating runners tends to be higher than that of normally menstruating nonrunning controls. Furthermore, female runners who are amenorrheic have higher bone mineral contents than untrained women who are amenorrheic. Thus, when we compare women of like menstrual status, those who are exercising will have the higher bone mineral content. Caution should be used in interpreting data such as those presented in this section, because the results can be confounded by such factors as body composition, age, height, weight and diet.

Although the precise mechanism is unknown, estrogen deficiency appears to play a major role in the development of osteoporosis. In the past, estrogen has been prescribed in an effort to reverse the degenerative effects of osteoporosis, but this therapy can have serious side effects, such as an increased risk of endometrial cancer. To reduce the risk, estrogen is given in combination with progestin(hormone replacement therapy, or HRT). However, there is an increased risk of breast cancer, strokes, and heart attacks associated with the use of HRT. Bisphosphonates, considered antiresorptive medications, are also used. Increasing calcium intake to 1,200 to 1,500 mg per day also has been proposed for decreasing the risk of osteoporosis.

Evidence certainly suggests that increased physical activity and adequate calcium intake combined with adequate caloric intake are a sensible approach to preserving the integrity of bone at any age.  However, maintaining normal menstrual function is critical for those who have not reached menopause.