A possible association between waist-to-hip ratio and cognitive function among Japanese health-checkup participants: an exploratory cross-sectional study

The association between obesity-related indices and cognitive function remains unclear, particularly when considering muscle mass. In this cross-sectional study, we examined these associations in 263 Japanese adults aged ≥ 40 years who underwent a health-checkup (163 males and 100 females). Cognitive function was assessed using the Japanese version of the Montreal Cognitive Assessment (MoCA-J), and obesity-related indices included body mass index, waist-to-hip ratio (WHpR), and other measures of obesity. Among males, WHpR was not significantly associated with MoCA-J scores after adjustment for age and lifestyle factors, whereas an inverse association emerged after additional adjustment for muscle mass. In the fully adjusted model, a higher WHpR was modestly associated with a lower MoCA-J score (standardised coefficient = − 0.17, P = 0.043) and higher odds of mild cognitive impairment (adjusted odds ratio = 1.08; 95% confidence interval, 1.00–1.16). No significant associations were observed among females. These findings suggest a possible modest association between WHpR and cognitive vulnerability in males when muscle mass is taken into account. However, the WHpR × sex interaction was not statistically significant, and the associations in males were borderline. Accordingly, this pattern should be interpreted as exploratory and hypothesis-generating rather than as evidence of any confirmed sex-specific effect. Trial registration: This study was registered in the University Hospital Medical Information Network (UMIN) Clinical Trial Registry on July 1, 2022 (UMIN000048056).