Context: Rates of bone loss across the menopause transition, and factors associated with variation in menopausal bone loss are poorly understood.

Objective: To assess rates of bone loss at each stage of the transition and examine major factors that modify those rates.

Design, Setting, and Participants: Longitudinal, cohort study of 1902 African-American, Caucasian, Chinese, or Japanese women participating in The Study of Women's Health Across the Nation (SWAN). Women were pre- or early perimenopausal at baseline.

Outcome Measure: Bone mineral density (BMD) of the lumbar spine and total hip across a maximum of 6 annual visits.

Results: There was little change in BMD during the pre- or early perimenopause. BMD declined substantially in the late perimenopause, with an average loss of 0.018 and 0.010 g/cm²/year from the spine and hip, respectively (P<0.001 for both). In the postmenopause, rates of loss from the spine and hip were 0.022 and 0.013 g/cm²/year, respectively (P<0.001 for both). During the late peri- and postmenopause bone loss was approximately 35–55% slower in women in the top versus the bottom tertile of body weight. Apparent ethnic differences in rates of spine bone loss were largely explained by differences in body weight.

Conclusions: Bone loss accelerates substantially in the late perimenopause and continues at a similar pace in the first postmenopausal years. Body weight is a major determinant of the rate of menopausal BMD loss whereas ethnicity, per se, is not. Health care providers should consider this information when deciding when to screen women for osteoporosis.