DETERMINANTS OF BONE-MINERAL DENSITY IN POSTMENOPAUSAL WHITE IOWANS

Background, Osteoporosis is a major health problem for older individua ls. For women, development of osteoporosis is a function of the accret ion of ''peak'' bone mass in the third decade, age at menopause, and r ate of bone loss with aging. Low bone mineral density (BMD) is a major risk factor for osteoporosis and fracture. The purpose of this study was to identify life style, nutritional, medical, and genetic predicto rs of low BMD in postmenopausal Iowa women. Methods. One hundred thirt y-four postmenopausal White women ranging in age from 57 to 81 years w ere included in this case-control study. Bone mineral density was meas ured at the Femoral neck, using dual photon X-ray absorptiometry (Holo gic 2000 QDR). Sixty-six women with BMD measurements below 0.68 g/cm(2 ) (the bottom quartile of the BMD distribution in the population from which participants were recruited), and 68 women with values at or abo ve 0.83 g/cm(2) (the top quartile of the BMD distribution in the same population) were included. Information about environmental, nutritiona l, medical, and life style modifiers of BMD was obtained by written qu estionnaire and telephone interview. To assess familial factors that m ight influence BMD, we obtained a derailed family history for each par ticipant. In addition, we tested the hypothesis that allelic variation at the Vitamin D receptor (VDR), and the type I collagen gene (COL1A1 and COL1A2) loci influence BMD. Results. Weight, loss of height, age, and age at menopause were strong predictors of BMD in our population. After adjustment for these differences, we found no effect of genotyp e at the COL1A1, COL1A2, and VDR loci on BMD. Conclusions, Bone minera l density is a complex trait that is influenced by several different m odifiers; in the present study, weight was the best predictor of postm enopausal BMD. While several studies suggest that VDR genotype is an i mportant determinant of BMD, we did not find this association in our p opulation, nor did we identify an association between allelic variatio n at the type I collagen gene loci and BMD. Identification of genes th at determine body mass index may provide additional insight into risk factors for low BMD, and osteoporotic fractures.