Introduction We examined how body mass index (BMI) over the life-course influences the risk of later life knee osteoarthritis (OA), for example, whether knee OA risk accumulates with prolonged exposure to high BMI or whether later rather than earlier adult life is the key period of exposure.
Methods A population-based birth cohort study of 3035 men and women who underwent a clinical examination for knee OA at age 53. BMI was measured 10 times from 2 to 53 years. Analyses were stratified by gender and adjusted for occupation and activity levels.
Results The prevalence of knee OA was higher in women than men—12.9% (n=194) vs 7.4% (n=108). In men, the association between BMI and knee OA was apparent at age 20 (p=0.038) and remained until 53 yrs (OR per z-score: 1.38; 95% CI 1.11 to 1.71). In women, there was evidence for an association at 15 yrs (p=0.003); this became stronger through adulthood- at age 53 the OR was 1.89 (CI 1.59 to 2.24) per z-score increase in BMI. A structured modelling approach to disentangle the way in which BMI over life influenced knee OA risk suggested that in women, prolonged exposed to high BMI throughout adulthood carried the highest risk, while in men, it was exposure in mid adulthood that explained most of the risk.
Conclusion Our study suggests that, particularly in women, the duration of exposure to high BMI in adulthood is important in explaining knee OA risk, and that these associations originate from weight gain in childhood and adolescence.
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