The role of duration on the association between obesity and risk of physical disability

INTRODUCTION : Obesity has been demonstrated to increase the risk of physical disability. With prevalence of obesity increasing in young and middle age groups amidst an ageing population, it is important to know if the association between obesity and disability is impacted by the duration of obesity. We aimed to relate obesity duration in mid-life with subsequent incidence of physical disability.

METHODS:   Study population: Framingham Offspring Study (FOS) participants aged 45-65years at examination 4 (1987-1991; “baseline” for our analysis). Obesity was defined by body mass index (BMI) >=30kg/m².  Obesity duration was calculated during the 20 years between examination 1 (1971-1975) through to examination 4. Disability data (defined as any limitation to at least one of eating, bathing, dressing, transferring, toileting and walking 50 yards) was available at examinations 5 (1991-1995) through 7 (1998-2001). Cox regression was used, first adjusting for age, sex and smoking followed by additional adjustment for baseline BMI. Participants were followed up to the development of disability, or censored at death or the end of the follow up period.

RESULTS: Of 2281 participants, 223 reported disability (incidence rate = 6 per 1000 person years). Obesity duration ranged from zero to 17 years (mean of 1.7 years (total population); 6.9 years (with baseline obesity)). When adjusted for age, sex and smoking, obesity duration was associated with an increased risk of disability (HR 1.06 per year of obesity; 95% confidence interval (CI) 1.04, 1.09). This association was attenuated on further adjustment for baseline BMI with borderline significance (HR 1.02 95% CI 0.98-1.05). The same was observed when analysis was restricted to those with baseline obesity.

CONCLUSIONS: There is a suggestion that obesity duration increases the risk of disability over and above BMI. Future work with longer durations is needed to explore the possibility that duration has an independent effect on the association between obesity and disability.