Background: Evidence on factors influencing the association between physical activity (PA) and knee osteoarthritis (KOA) is scarce. The present study aimed to examine this association and explore interactions of PA with sex and age in relation to KOA in Japanese adults.
Methods: This 11-year cohort study included 10,876 community-dwelling individuals aged 40-74 years in Murakami City (Niigata Prefecture, Japan). Data were collected using a self-administered questionnaire (2011-2013). Exposures were self-reported PA levels, and the outcome was clinically diagnosed KOA. Covariates included demographic factors, body size, lifestyle habits, and disease history. Cox proportional hazards models were used to estimate hazard ratios (HRs).
Results: The mean age of participants was 58.0 years. Over a mean follow-up period of 11.1 years, 840 cases of KOA were observed. High total PA levels were associated with a greater KOA risk (P for trend <0.0001), with the highest quartile showing a higher hazard (HR=1.52, 95%CI:1.23-1.87) than the lowest (reference). This association was observed in both males (HR=2.01, 95%CI:1.39-2.93) and females (HR=1.30, 95%CI:1.01-1.66), with a P for interaction of 0.0219. In addition, the association was more pronounced in younger participants (<55 years; HR=2.07, 95%CI:1.25-3.43) and attenuated in older age groups, with a P for interaction of 0.0278. Non-leisure-time PA showed a similar association with KOA as total PA, whereas leisure-time PA did not.
Conclusion: High total and non-leisure-time PA levels were associated with increased KOA risk, and these associations interacted with sex and age in middle-aged Japanese adults.
Keywords: cohort study; knee osteoarthritis; physical activity; risk factor.