Associations of obesity phenotypes with incident fall rates: results from the objective physical activity and cardiovascular disease health in older women study

Background: Obesity and sarcopenia may influence fall risk through different mechanisms, but how different phenotypes affect fall rates is unclear, especially among older women. This study examined associations of whole-body obesity, abdominal obesity, and sarcopenic obesity with incident fall rates among community-dwelling older women in the United States. Methods: We analyzed data from 4654 ambulatory women aged ≥63 years in the Objective Physical Activity and Cardiovascular Health study, an ancillary study of the Women’s Health Initiative. Whole-body overweight and obesity were defined as body mass index (BMI) 25 to <30 kg/m² and ≥30 kg/m², respectively; abdominal obesity as waist circumference >88 cm; and sarcopenia as grip strength <20 kg. Sarcopenic obesity was defined as the coexistence of obesity (either whole-body or abdominal) and sarcopenia. Falls were recorded using daily calendars over 13 months. Negative binomial regression models estimated associations between obesity phenotypes and monthly fall rates, adjusting for demographic, behavioral, and health-related covariates. Results: Whole-body overweight and obesity were associated with lower fall rates compared to normal BMI (overweight incidence rate ratio [IRR] = 0.82, 95% confidence interval [CI] = 0.73, 0.92; obesity IRR = 0.76, 95% CI = 0.66, 0.87). Abdominal obesity showed a modest association with reduced fall rates (IRR = 0.87, 95% CI = 0.78, 0.96). In contrast, sarcopenia alone (IRR = 1.44, 95% CI = 1.24, 1.68), and sarcopenic obesity (IRR = 1.20, 95% CI = 1.03, 1.39) were associated with significantly higher fall rates. Conclusions: Our findings underscore the critical role of muscle strength loss, rather than excess adiposity, in fall risk among older women. Future interventions to reduce sarcopenia may reduce fall rates.