Challenging the obesity paradox in cognitive function: Weight‐adjusted waist index as an obesity indicator in older adults

AIMS: Midlife obesity is a known risk factor for cognitive impairment, whereas its association in late life is complex, giving rise to the concept of the 'obesity paradox.' The weight-adjusted waist index (WWI), an indicator reflecting central obesity, has recently emerged. However, evidence regarding the association between WWI and cognitive impairment in Chinese older adults remains scarce. This study explores WWI's association with cognitive decline in older adults, addressing gaps in central obesity's role in neurocognitive health. MATERIALS AND METHODS: A total of 5001 older adults aged ≥65 years with normal cognition from the Chinese Longitudinal Healthy Longevity Survey were included in this longitudinal analysis, with a median follow-up duration of 4 years. A time-varying Cox proportional hazards regression model was used to evaluate the association between WWI, waist circumference (WC), body mass index (BMI) and incident cognitive impairment. Nonlinear correlations were investigated using restricted-cubic-spline curves. Subgroup analyses and sensitivity analyses were conducted to enhance the robustness of findings. RESULTS: The incidence of cognitive impairment across the four WWI quartile groups (Q1-Q4) was 6.7%, 7.8%, 9.3% and 13.4%, respectively. WWI was positively associated with incident cognitive impairment, whether treated as a continuous variable (hazard ratio [HR] = 1.14, 95% confidence interval [95% CI] = 1.06-1.23) or a categorised variable (Q4 vs. Q1: HR = 1.70, 95% CI = 1.29-2.24; Q3 vs. Q1: HR = 1.43, 95% CI = 1.08-1.90) in models adjusted for multiple covariates. WC showed a similar trend, while BMI demonstrated no significant association. Associations persisted across subgroups and sensitivity analyses. CONCLUSIONS: Elevated WWI and WC, but not BMI, were significantly associated with an increased risk of incident cognitive impairment. The findings suggested that WWI may be a more precise indicator of the association between obesity and cognitive impairment.