Risk factors for osteoporosis: prevalence, change, and association with bone density.

Objectives: To describe the prevalence of risk factors for osteoporosis in a population-based cohort of Australian-born midlife women; determine the effect of these risk factors on premenopausal and early perimenopausal bone mineral density (BMD); and describe changes in risk factors and any effect of these on bone loss.

Design: 4-year longitudinal community-based study. BMD of the lumbar spine (LS) and femoral neck (FN) was measured using dual x-ray absorptiometry (DXA).

Setting: Melbourne, Australia

Participants: 224 Australian-born women aged 46-56 years

Main outcome measures: Risk factors for osteoporosis, LS-BMD, FN-BMD, and change in risk factors and BMD.

Results: At baseline, 52% reported a calcium intake of less than 800 mg/day and 46% reported a caffeine intake of more than 360 mg/day; 29% exercised less than 1.5 hours/week; 5% had a body mass index (BMI) of less than 20; 14% were current smokers; 23% were past smokers; 10% reported abnormal menstrual histories; and 25% reported a family history of osteoporosis. BMD was positively associated with weight; BMI; and waist, hip, and trunk skin-fold measure (P less than .0005). At 4-year follow-up, there were increases in weight (P less than .0005), waist/hip ratio (P less than. 05), trunk skin-fold measurements (P less than.005), and calcium intake (P less than.05). In women who became late perimenopausal or postmenopausal, bone loss was associated with time in relation to the final menstrual period but not with other variables.

Conclusions: There are multiple risk factors for osteoporosis in this Australian-born population of midlife women, but only anthropometric variables were associated with BMD at baseline. Significant changes during the menopausal transition in anthropometric variables and calcium intake were in the direction that could decrease the risk of osteoporosis but were not found to affect menopausal bone loss.