Abstract
BackgroundKnee osteoarthritis (kOA) risk is increased by obesity and physical activities (PA) which mechanically stress the joint. We examined the associations of midlife kOA with body mass index (BMI) and activity exposure across adult life and their interaction.MethodsData are from a UK birth cohort of 2597 participants with a clinical assessment for kOA at age 53. At ages 36, 43 and 53 BMI (kg/m2), self-reported leisure-time PA, and occupational activity (kneeling/squatting; lifting; climbing; sitting; assigned using a job-exposure matrix) were ascertained. Associations were explored using the multiplicative logistic model.ResultsBMI was strongly and positively associated with kOA in men and women. Men and women in manual occupations also had greater odds of kOA; there was a weak suggestion that kOA risk was higher among men exposed to lifting or kneeling at work. For men, the only evidence of a multiplicative interaction between BMI and activities was for lifting (p = 0.01) at age 43; BMI conferred higher kOA risk among those most-likely to lift at work (OR per increase in BMI z-score: 3.55, 95% CI: 1.72-7.33). For women, the only evidence of an interaction was between BMI and leisure-time PA (p = 0.005) at age 43; BMI conferred higher kOA risk among those at higher PA levels (OR per increase in BMI z-score: 1.59, 95% CI: 1.26-2.00 in inactive; 1.70, 95% CI: 1.14-2.55 (less-active); and 4.44; 95% CI: 2.26-8.36 (most-active).ConclusionsAt the very least, our study suggests that more active individuals (at work and in leisure) may see a greater reduction in risk of kOA from avoiding a high BMI than those less active.
Highlights
Knee osteoarthritis risk is increased by obesity and physical activities (PA) which mechanically stress the joint
While studies have shown that body mass index (BMI) and occupational activity are independently associated with Knee osteoarthritis (kOA) risk in a multiplicative model [6,7,18,19], only one has shown evidence for a positive multiplicative interaction [6]
Lifting and kneeling occupational activities were more common than climbing or walking, and approximately 70% of participants were in occupations which involved sitting for ≥ two hours/day
Summary
Knee osteoarthritis (kOA) risk is increased by obesity and physical activities (PA) which mechanically stress the joint. Given recent trends demonstrating a global increase in mean BMI over the past 30 years [17], it is important to consider whether the influence of BMI on kOA is dependent on other potentially modifiable risk factors such as occupational and leisure-time physical activity across life course. Studies examining both physical activity and BMI are less convincing [20,21,22,23,24,25]; only one found evidence of a multiplicative interaction [26] and some report no evidence of an association between physical activity and kOA independent of BMI [23,25] Many of these studies have been retrospective or case–control [6,7,18,20,22], potentially suffering from differential recall bias which would inflate associations. To our knowledge there are no prospective population based studies examining the intersecting nature of BMI with activity at particular ages in midlife and few studies have examined this relationship with relatively early onset of kOA
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