Sleep quality and weight-adjusted waist index in US adults: a cross-sectional study from NHANES 2015-2020

Sleep quality, independent of sleep duration, has been linked to central obesity. However, prior findings are inconsistent, likely due to reliance on body mass index and waist circumference, which inadequately capture abdominal fat. The weight-adjusted waist index offers a more sensitive, size-adjusted measure of central adiposity. Therefore, this study aimed to examine the association between sleep quality and weight-adjusted waist index in a nationally representative population.

We analyzed secondary data from 8,718 adults aged ≥20 years in the 2015-2020 National Health and Nutrition Examination Survey (NHANES). Sleep quality was assessed using a self-reported questionnaire and treated as both continuous and categorical (low, medium, high). The weight-adjusted waist index was calculated as waist circumference (cm) divided by the square root of body weight (kg). Linear regression models were used to estimate associations between sleep quality and weight-adjusted waist index across four models with progressive adjustments: demographics (age, sex, race/ethnicity), health insurance and socioeconomic status, lifestyle behaviors, and chronic conditions.

Higher sleep quality was associated with lower weight-adjusted waist index. Each model increases in sleep quality score corresponded to lower weight-adjusted waist index (β = -0.21, p < 0.001 in unadjusted; β=-0.05, p = 0.001 fully adjusted). In categorical variables, high sleep quality remained protective after full adjustment (β=-0.11, p = 0.001), while medium quality was non-significant. Subgroup analyzes showed stronger associations among younger adults, women, and non-Hispanic Whites, but weaker among older adults and minority groups. No significant interactions were observed for marital status, sedentary behavior, smoking, alcohol use, or chronic conditions.

This is the first study to demonstrate an independent inverse association between sleep quality and weight-adjusted waist index in a nationally representative U.S. sample. Improving sleep quality may serve as a modifiable strategy to reduce central adiposity and related cardiometabolic risk.