1Department of Human Evolutionary Biology, Harvard University, 2Department of Anthropology, University of New Mexico, 3Rheumatology Section, Boston University School of Medicine, 4Institute for Quantitative Social Science, Harvard University, 5Department of Radiology, Brigham and Women’s Hospital, 6Department of Anthropology, University of Oregon, 7Cardiovascular Performance Program, Massachusetts General Hospital
April 16, 2020 56, Platinum Ballroom
Because obesity is a primary risk factor for knee osteoarthritis (OA), non-industrial societies with low obesity levels are expected to have low levels of knee OA. However, individuals born under conditions of limited energy availability have been shown to be predisposed to accumulate excess abdominal (visceral) adipose tissue if they subsequently encounter lifestyle changes that promote positive energy balance. We therefore hypothesized that individuals in non-industrial societies undergoing an energy balance transition may have larger abdomens relative to body weight and hence a heightened risk of knee OA for a given body mass index (BMI). We tested this hypothesis by comparing knee radiographs and anthropometry among males aged ≥40 years from two populations: Tarahumara subsistence farmers in Mexico undergoing an energy balance transition (n=157) and urban Americans from Framingham, Massachusetts (n=565). We found that average BMI among Tarahumara and Framingham individuals was 24 and 29 kg/m2 and the probability of obesity was 6% and 41%, respectively. However, controlling for body weight, average abdomen circumference among Tarahumara and Framingham individuals was 109 and 99 cm, respectively. Due to their relatively low-BMI, large-abdomen phenotype, the Tarahumara had 13% higher probability of knee OA for a given age and BMI than Framingham individuals. Moreover, knee OA probability increased more markedly with greater abdomen size among Tarahumara than Framingham individuals. These findings indicate that knee OA risk among non-industrial societies experiencing an energy balance transition is potentially much greater than presumed, which is alarming since such populations constitute much of the global population.