Osteoporosis in elderly men and women: Effects of dietary calcium, physical activity, and body mass index

Dietary calcium intake and physical activity are considered practical measures for prevention of osteoporosis. However, their associations with bone mineral density (BMD) in the elderly are not clear. The present study examined the association between osteoporosis and these two factors in relation to body mass index (BMI) in a cross-sectional, epidemiological study involving 1075 women and 690 men, aged 69 +/- 6.7 years (mean +/- SD). Dietary calcium intake (median of 580 mg/day) was inversely related to age (p = 0.01), positively related to physical activity index (PAI) (p = 0.01), femoral neck BMD (p = 0.01) in women, and higher lumbar spine (p 0.003) and femoral neck BMD (p = 0.03) in men. Quadriceps strength was negatively associated with age (p < 0.0001) and positively related to BMI (p < 0.0001) and BMD (p < 0.0001) in both men and women. The PAI was associated with quadriceps strength (p < 0.0001) and femoral neck and lumbar spine BMD in women (p < 0.001) and with femoral neck BMD in men (p = 0.04); however, these associations were not significant after adjusting for age, BMI, quadriceps strength, and dietary calcium. Women in the top tertile of quadriceps strength (greater than or equal to 23 kg) and dietary calcium intake (greater than or equal to 710 mg/day) had 15% higher BMD than those In the lowest tertiles (less than or equal to 15 kg and less than or equal to 465 mg/day); the difference was comparable in men (11%). Among subjects with the lowest tertiles of BMI (less than or equal to 23 kg/m(2) for women and less than or equal to 24 kg/m(2) for men), quadriceps strength (less than or equal to 15 kg for women and less than or equal to 28 kg for men), and dietary calcium intake (less than or equal to 465 mg/day), 64% and 40% of women and men, respectively, were classified as having osteoporosis (based on a 2.5-SD reduction from the young-normal mean). The prevalence was only 12% in women and 1.5% in men among those in the highest tertiles of the three factors. Adequate dietary calcium intake and maintaining a physically active lifestyle in late decades of life could potentially translate into a reduction in the risk of osteoporosis and hence improve the quality and perhaps quantity of life in the elderly population.