Bone Loss at the Femoral Neck in Premenopausal White Women: Effects of Weight Change and Sex-Hormone Levels

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This study measured bone mineral content (BMC), bone mineral density (BMD), and bone area at the spine and hip to learn whether bone loss takes place premenopausally. Participants were 130 non-Hispanic white women 31 to 50 years of age who were in good general health and had taken no drugs that affect bone metabolism. Measurements were made by dual-energy x-ray absorptiometry at the L2-4 segment of the lumbar spine, in the femoral neck, and in the total hip. The studies were repeated at least twice over 1 to 9 years. Both BMC and bone area increased significantly over time in the spine, as did BMD. If, however, BMC was normalized by bone volume, there was no age-related change in volumetric density. Measurements of the total hip showed no significant change with age. BMD in the femoral neck declined at a rate of about 0.0036 g/cm2 per year. BMC was lost as well, so the drop in BMD was not an artifact of bone expansion. Changes in BMD correlated positively with weight change and estradiol levels and negatively with gonadotropin levels. Somewhat less bone loss was noted in subjects who gained more weight during the study. Higher levels of LH and FSH were documented in women who lost more than 1% of BMD per year. Estrogen levels were highest in women who manifested no bone loss. Declining BMD was more a result of a loss of BMC in women with high FSH levels, but due more to an expansion in bone area in those with relatively low FSH levels. The positive association between body weight change and BMD was not entirely mediated by higher estrogen. Premenopausal women more than 30 years of age in this study lost BMD at the femoral neck at an average annual rate of 0.4%. Bone loss was less in women who gained more weight but greater in those with reduced estrogen levels even in the absence of symptoms. Early bone loss might be preventable if premenopausal women with suboptimal sex hormone levels are detected at an early stage.