Levels of the proinflammatory adipokine leptin contribute nearly half of the total effect of obesity on knee osteoarthritis (OA), according to a study using two different methods of mediation analysis. These findings add to the accumulating evidence of a pathogenetic role for metabolic factors (including leptin) in knee OA. Baseline data on BMI and serum leptin levels were obtained from 653 community-dwelling adults aged ≥70 years who participated in the population-based MOBILIZE Boston Study. In adjusted regression models, a 5 kg/m2 increase in BMI was associated with a 32% increase in the probability of OA, and a 200 pM increase in serum leptin was associated with an 11% increase in the probability of OA. Fat mass might be more predictive of knee OA than BMI, the researchers write.