Effects of physical activity and dietary calcium intake on bone mineral density and osteoporosis risk in a rural Thai population.

The objective of the study was to determine the effects of modifiable risk factors on bone mineral density in postmenopausal Thai women. Dietary calcium intake (g/day), energy expenditure (kcal/day), and sunlight exposure (h/day) were assessed in 129 rural Thai women aged 63 years (range 50 to 84 years). Bone mineral density (BMD) at the femoral neck, lumbar spine, and distal radius were measured by dual-energy X-ray absorptiometry (DXA). The average dietary calcium intake was 236 +/- 188 g/day (mean +/- SD), while the energy expenditure was 2,118 +/- 656 kcal/day with 1.1 +/- 1.7 h of sunlight exposure. In multiple linear regression analysis, dietary calcium intake, energy expenditure, and years since menopause were significant and independent predictors of BMD at various sites. The three factors together accounted for between 35% and 45% of the variance of BMD. The prevalence of osteoporosis (defined as BMD T-scores < or =-2.5) was 33% at the femoral neck, 42% at the lumbar spine, and 35% at the distal radius. The risk of osteoporosis was higher in women with lower dietary calcium intake (< or =138 mg/day; prevalence rate ratio [PRR], 1.4; 95% confidence interval [CI], 1.0 to 1.9), lower energy expenditure (< or =1,682 kcal; PRR, 1.7; 95% CI, 1.2 to 2.3), and greater years since menopause (> or =6 years; PRR, 2.6; 95% CI, 1.2 to 5.8). The population attributable risk fraction of osteoporosis risk due to the three factors was 70%. These results suggest that in the Thai population, low dietary calcium intake and low physical activity together with advancing years since menopause were independent risk factors for low BMD.