The consequences of serum calcium homeostasis, reproductive life history and bone mineral content in postmenopausal women with implications to theories of aging

Abstract

Type I and II osteoporosis will become an increasingly common problem in years to come, since the population structure is changing with the graying of America. This study identifies anthropometric and reproductive variables known to affect bone mineral in a mixed cross-sectional and longitudinal retrospective study. Data were collected from 3120 women and 1222 men throughout Arizona by single photon absorptiometry of the distal third of the radius by Lunar software for bone width, bone mineral content and bone mineral density and anthropometric, reproductive, nutritional and fracture histories. With age-stratified and age-adjusted statistical analyses, important relationships are found to exist between these variables. In females, the anthropometric variables--age, height and weight--are highly correlated with distal third radial width, bone mineral content and density. In males, weight is correlated with distal third radial width; age and weight with bone mineral content; and age, height and weight with bone mineral density. Reproductive variables--age, age at menarche and menopause and total reproductive span--are predictors for women who undergo surgical oophorectomy and hysterectomy, but not those who undergo natural menopause or either surgery. Variables related to pregnancy--age, height, weight, pregnancy duration and span--are predictors of distal third radial width. Only age, height and weight are predictors of bone mineral content. Age, height, weight, age at last pregnancy and one derived ratio are predictors of bone mineral density. When variables related to breastfeeding are incorporated, pregnancy duration and derived ratios are identified for predictors of distal third radial width. Only one ratio is related to bone mineral content, whereas pregnancy number, pregnancy and breastfeeding duration and derived ratios are useful predictors of bone mineral density. These findings suggest that pregnancy and breastfeeding leave lasting effects on bone mineral. While techniques exist to measure bone mineral in various locations, the distal third of the radius is more trabecular than some sites (e.g., the femoral head and vertebral centra). With such changes documented in the radius, more extreme effects are expected at more trabecular locations. Thus, a life's reproductive history is etched in bone.