The Relationship between Body Mass Index and Bone Mineral Density in Older People

Osteoporosis and obesity are a world major problem that their prevalence is increasing. Obesity is a risk factor for cardiovascular and metabolic diseases although it is said that it has protective effect on bone loss. The aim of this study was to evaluate the relationship between body mass index and bone mineral density in older people.

This cross sectional study came from "Amirkola Health and Aging Project (AHAP)" that has been done on 1000 people aged 60 and over in Amirkola city, Iran. Demographic data collected by questionnaire. Weight, height, waist circumference and hip circumference were measured. Waist to hip ratio (WHR) and body mass index (BMI) were calculated and bone mineral density (BMD) was measured by DEXA scan in lumbar spine and femoral neck.

In this study, 554 (55.4%) of the participants were men and 446 (44.6%) were women. The mean of bone mineral density in femur (0.90±0.1) and spine (0.94±0.2) in men were higher than women (0.80±0.1 versus 0.79±0.1 respectively) (p=0.001). BMI has significant positive relationship with BMD (p=0.001) that in both men and women this relationship was strongest in femoral neck (p=0.001). Central obesity in men had a positive association with bone mineral density in both areas (p=0.000). In overall the strongest relationship of femoral neck BMD was with BMI (r=0.38, p=0.001) and in lumbar spine was with WHR (r=0.21, p=0.001). Regression analyses showed that by control of age, WHR and waist circumference, BMI is effective on femoral neck BMD but in lumbar spine the effect of BMI has covered with those factors.

Due to high prevalence of osteoporosis in older people with lower BMI, having normal weight in older people is recommended to prevent decreasing bone mineral density.