A United Kingdom perspective on the relationship between body mass index (BMI) and bone health: a cross sectional analysis of data from the Nottingham Fracture Liaison Service

Abstract

Objectives: This study examines the relationship between high BMI, a diagnosis of osteoporosis and low trauma fractures.

Method: This is a cross sectional analysis using data collected from the Nottingham Fracture Liaison Service. A total of 4288 participants with a low trauma fracture from 1 January 2007 to 31 August 2012 were analysed. Logistic regression adjusted for potential confounders was used investigate osteoporosis and BMI. Fracture types were compared between those who were obese and non-obese.

Results: A total of 30% (1285) were obese. Prevalence of osteoporosis was 13.4%, 24.9%, and 40.4% in the obese, overweight and normal category respectively. Being obese has an odds ratio of 0.23 (95% CI 0.19-0.28, p<0.01) of having osteoporosis compared to a normal BMI category. When variable BMI cut offs were used (BMI 25, 30 and 35) to calculate the positive predictive value of patients not having osteoporosis, it was 80.5%, 86.3% and 88.3%. Examining fracture types, obese patients when compared with the non-obese category, were more likely to fracture their ankle (OR 1.48, p<0.01) and upper arm (OR 1.48, p<0.001), but were less likely to fracture their wrist (OR 0.65, p<0.001). In the elderly (>70years), obesity no longer influenced ankle or wrist fractures but there is an increased risk of upper arm fractures (OR 1.46, p=0.005).

Conclusion: Higher BMD in obesity is not protective against fractures as there are a significant number of fractures in this group which may be due to body habitus, mechanism of injury and the effect of adiposity on bone. A low trauma osteoporotic fracture will need to be redefined in light of these findings.

Keywords: Body mass index; Bone density; Bone fractures; Bone fragility; Obesity; Osteoporosis.