Association of body mass index and hip fracture has been controversial. In this study, women with lowest and highest body weight had the highest fracture incidence. A 25-year follow-up indicated that obesity associates with early hip fracture risk and suggested increasing trend in normal-weight women at a later stage.
Introduction: Obesity is a pandemic health issue. Its association with hip fracture risk remains controversial. We studied the long-term relationship of body mass index and hip fracture incidence in postmenopausal women.
Methods: The cohort of 12,715 Finnish women born in 1932-1941 was followed for 25 years, covering ages from 58 up to 83. Fractures and deaths were obtained from national registries. Women were investigated in deciles of BMI as well as in WHO weight categories (normal, overweight, or obese). The follow-up analysis was carried out in two age strata as "early" (58-70 years) and "late" (> 70 years). Body weight information was updated accordingly. Femoral neck BMD was recorded for a subsample (n = 3163). Altogether, 427 hip fractures were observed.
Results: A higher risk of early hip fracture was observed in obese and normal-weight compared with overweight women with hazard ratios (HRs) of 2.3 ((95% CI) 1.4-3.7) and 2.0 (1.3-3.1) while no difference was observed in late hip fracture risk between the three WHO categories (log rank p = 0.14). All-cause mortality during the follow-up was 19.3%. Compared with normal weight women, the obese women had a higher risk of death with an HR of 1.6 (1.4-1.8) and higher baseline BMD (p < 0.001). Faster bone loss was observed in the obese compared with other women (p < 0.001).
Conclusion: Obesity associates with earlier hip fracture and higher postfracture mortality. The obese women with low BMD have clearly the highest risk of hip fracture. This combination increases hip fracture risk more than either of the factors alone. After 75 years of age, risk appears to increase more in normal weight women, but this trend is in need of further confirmation.
Keywords: Aging; Body mass index; Bone mineral density; Follow-up study; General population; Hip fracture; Menopause; Obesity.