The effect of sex steroids on the skeleton in premenopausal women Robert Lindsay, MB, ChB, PhD, FRCP West Haverstraw and New York, New York Whereas peak bone mass is genetically determined, the skeletal growth, maturation, and maintenance required to reach this peak may be influenced by physical activity, ovarian function, and nutrition. Estrogen deficiency at menopause leads to increased skeletal remodeling and loss of bone mass, which can result in osteoporotic fractures. Entering menopause with low bone mass is a risk factor itself, because bone mass predicts future risk of fracture. The administration of exogenous steroids can reverse the setting of the "mechanostat" to lower levels after ovarian dysfunction, although it is unclear whether oral contraceptives can modify bone mass in the ovulatory premenopausal woman. Our recent data suggest that the use of steroidal hormones to treat menstrual irregularity (presumably relative to ovarian dysfunction), as opposed to fertility control, is more likely to positively affect bone mass. It is even less clear whether hyperestrogenic states (e.g., pregnancy) affect the skeleton. Recent evidence from bone mass changes that occur in women with ovulatory cycles and inadequate luteal phase function suggests that progestins may also influence skeletal metabolism. (AM J OSSTET GVNECOL 1992;166:1993-6.)

Key words: Peak bone mass, ovarian function, osteoporotic fractures

Bone mass or density in adult life is the algebraic sum of the amount of bone mass accumulated during growth and its subsequent alteration by a variety of factors that change skeletal behavior and modify bone mass. The best known factor is cessation of ovarian function at menopause, which increases skeletal remodeling and accelerates the rate of bone loss.':" The consequence-increased risk of osteoporotic fractures among postmenopausal women-is equally well known. Increasing evidence indicates that entering menopause with low bone mass is itself a risk factor, because bone mass at any time can predict future fracture risk. To date comparatively little attention has been given to those factors that might modify skeletal mass in premenopausal women and alter their risk of osteoporotic fracture before they enter menopause. Onset of menopause would then become a signal for the physician to evaluate the patient's potential risk of fracture. This review evaluates the factors that might change skeletal mass and thereby alter skeletal integrity in women before they reach menopause. Peak bone mass Although the amount of bone in the skeleton at the end of linear growth is primarily genetically deter-

From the Helen Hayes Hospital, Regional Bone Center and Columbia University College of Physicians and Surgeons. Supported in part by Public Health Service grants AR39191 and DK42392. Reprint requests: Robert Lindsay, MB, ChB, PhD, FRCP, Helen Hayes Hospital, Route 9W, West Haverstraw, NY 10993.

610137612

mined," the potential to reach peak bone mass may be modified by several factors. Many of these factors are similar to those that are known to modify skeletal mass in adult life, including nutrition, physical activity, and intercurrent illness. The importance of these factors has been determined mainly by studying the effects of extremes. For example, paralysis during childhood leads to development of bone mass that, while adequate for the stress placed on the skeleton in a paralyzed person, is clearly inadequate to withstand the stresses that might be placed on it during normal activity.' Extremes of nutritional aberration, such as anorexia and bulimia, deprive the skeleton just as they deprive the remainder of the body of essential nutrients." 9 Malabsorption syndromes effect the same process. 10 In growing children the roles of nutrition and a normal life-style in modifying peak bone mass have been inadequately studied. Preliminary data from one study" suggest that calcium intake increases bone mass in teenagers. In this study the effects of calcium supplements that were given to one twin of a series of monovular twin pairs were examined. The findings reveal greater skeletal mass in the twins who received supplementation. However, it is as yet unknown whether the subjects who have faster accretion will subsequently develop maximal (or peak) skeletal mass greater than that developed by the nonsupplemented twin. Thus the study will be incomplete until all twins have reached peak skeletal mass. The extent to which peak skeletal mass depends on physical activity within the normal ranges for growing children and teenagers is also unclear. 12 Again, this is-

1993

1994 Lindsay

Ju ne I Y92

Am J O bsret Gy nccol

o

~

en c

The effect of sex steroids on the skeleton in premenopausal women.

Whereas peak bone mass is genetically determined, the skeletal growth, maturation, and maintenance required to reach this peak may be influenced by ph...
492KB Sizes 0 Downloads 0 Views