Walking duration and habitual exercise related to bone mineral density using computer-assisted X-ray densitometry in Japanese women

Background: We conducted a survey to examine the difference in metacarpal bone mineral density (BMD) associated with the duration of walking and participation in habitual exercise in order to assess the benefits of walking for the prevention of bone loss in Japanese women. Methods: The subjects were 1873 healthy women (premenopausal, n = 1502; postmenopausal, n = 371), aged 18–72 years, who were screened for osteoporosis at health-care centers. They were classified into pre- (n = 1502), early post- (0–5 years since menopause, n = 195) and late post-menopausal (6–20 years since menopause, n = 176) phases. The metacarpal BMD was measured by computer-assisted X-ray densitometry. Subjects completed a questionnaire on lifestyle factors that included habitual exercise and daily walking time. To consider the factors of aging and physical characteristics, the BMD of all subjects was adjusted for age and height using a multiple non-linear model based on the data for premenopausal women. Results: anova indicated significant differences in adjusted BMD (BMDadj) in all menopausal phases according to walking duration and whether or not habitual exercise was engaged in. Premenopausal and early postmenopausal women who walked for over 30 min a day had a significantly greater BMDadj than those walking for less than 30 min (2.743 vs 2.684 mm thickness of an aluminum equivalent [mm Al]; and 2.711 vs 2.597 mm Al, respectively). Late postmenopausal women who walked for over 120 min had a significantly greater BMDadj than those walking under 30 min per day (2.746 vs 2.539 mm Al). Conclusion: These findings suggest that daily walks of more than 30 min also affect the metacarpal BMD, which is a non-weight bearing site, although walking over 120 min seems required to benefit late postmenopausal women. We conclude that such daily walks appeared to be beneficial in maintaining BMD in Japanese women.