An exploratory comparison of vertebral fracture prevalence and risk factors among native Japanese, Japanese-American, and Caucasian women

Abstract

In this cross-sectional population-based study, the prevalence of vertebral fractures in elderly women was compared among native Japanese in Hiroshima, Japanese-Americans in Hawaii, and North American Caucasians in Minnesota. Compared with Japanese-American women, the age-adjusted odds ratios for native Japanese women were significantly and consistently greater than 1.0 (range from 1.6 to 2.6, depending on fracture definition), while the age-adjusted odds ratios for Caucasian women living in Minnesota were closer to 1.0 (range from 0.5 to 1.5, depending on fracture definition). These data indicated that the age-adjusted overall prevalence of vertebral fracture among Japanese-American women was quite different from the prevalence in Japan, but more similar to the prevalence in the U.S., suggesting non-genetic factors may have some impact on vertebral fractures. Spine bone mineral density (BMD), a major predictor of vertebral fracture prevalence in this study, was found to be lower among native Japanese than among Japanese-American women even after adjusting for age. This difference was mainly due to the differences in body size and menstrual history between the two populations. On the average, native Japanese women were shorter and lighter, and tended to have a later menarche, an earlier menopause, and a shorter period between menarche and menopause. In linear regression analysis, age, weight and menstrual history (age at menopause or years between menarche and menopause) were found to be significantly associated with BMD, and thus might contribute to fracture risk indirectly through their effects on BMD. However, this study also shows that age and menstrual history provided complementary information about fracture risk and explained additional difference in fracture prevalence after adjusting for BMD, suggesting that BMD is a major but not a sole risk factor for vertebral fractures. Age-related and menopause-related mechanisms may also play an important role in spine fracture independent of BMD. The observed differences in vertebral fracture prevalence and related risk factors between native Japanese and Japanese-American women may be evidence for environmental effects, such as changes in nutrition and lifestyle.