A High Body Mass Index Protects Against Femoral Neck Osteoporosis in Healthy Elderly Subjects

Objective: In a large sample of elderly subjects, we assessed the possible protective effect of obesity on the development of osteoporosis.

Methods: Healthy subjects 70 y or older and of low socioeconomic level were studied. Bone mineral density was measured in the femoral neck by using a Lunar Prodigy double beam densitometer and compared measurements with appropriate standards. Osteoporosis was defined according to criteria of the World Health Organization (WHO). Body weight and height were recorded simultaneously, and body mass index (BMI) was calculated as weight (kg) divided by height (m2). Age-adjusted odds ratios for femoral osteoporosis were calculated for WHO-proposed BMI ranges in women and men, with an odds of one for a BMI below 25 kg/m2.

Results: Eight hundred forty-five subjects (615 women and 230 men; mean age, 75 +/- 4.4 y) were studied. Mean BMI was 28.1 +/- 4.7 kg/m2. Twenty five percent of women and 11% of men had osteoporosis (P < 0.001). Forward stepwise multiple regression analysis showed BMI to be the best independent predictor of bone mineral density in women and men. The age-adjusted odds ratios for femoral osteoporosis were 0.34 (95% confidence interval [CI], 0.21 to 0.55) and 0.13 (95% CI, 0.04 to 0.43) for women and men with a BMI between 25 and 30 kg/m2, respectively. The odds ratios for women and men with a BMI between 30 and 35 kg/m2 were 0.21 (95% CI, 0.11 to 0.39) and 0.09 (95% CI, 0.01 to 0.67), respectively

Conclusions: This study confirms the protective effect of a high BMI on femoral neck bone mineral density among elderly subjects. The risk for osteoporosis among men and women with a BMI above 30 kg/m2 was approximately 33% compared with subjects with a normal BMI.