**Background:** Nonalcoholic fatty liver disease (NAFLD) affects approximately 25% of the global population and is strongly linked to metabolic disorders such as obesity, diabetes, and dyslipidemia. While lifestyle interventions including diet and exercise are first-line treatments, the role of sleep in NAFLD pathogenesis remains controversial. Prior studies have reported conflicting associations between sleep duration, sleep quality, and NAFLD risk, with some showing increased risk with short sleep and others showing associations with long sleep. Sex differences have been suggested but not consistently examined.
**Methods:** This cross-sectional study enrolled 1,073 participants (282 with NAFLD, 791 without) from Lihuili Hospital of Ningbo Medical Center and its East Hospital between January and December 2018. Participants completed the Pittsburgh Sleep Quality Index (PSQI) and Munich Chronotype Questionnaire (MCTQ). Sleep duration was classified per 2015 National Sleep Foundation age-specific recommendations into too short, recommended, appropriate, and too long categories. Poor sleep quality was defined as PSQI > 5. NAFLD was diagnosed by hepatic ultrasonography. Multivariate logistic regression models were used to calculate odds ratios (OR) and 95% confidence intervals (CI) for NAFLD risk across sleep categories, with progressive adjustment for covariates including age, smoking, drinking, physical exercise, eating habits, BMI, and fasting plasma glucose (FPG).
**Key Results:** The NAFLD group was significantly older (41.30 ± 10.04 vs. 36.74 ± 10.92 years, P < 0.001), had higher BMI (25.86 ± 2.76 vs. 21.7 ± 2.72 kg/m², P = 0.036), and contained a higher proportion of men (89.72% vs. 58.03%, P = 0.001) compared to the non-NAFLD group. Smoking history (P = 0.027), eating habits (P = 0.009), and marital status (P = 0.033) also differed significantly between groups. No significant differences in sleep duration (P = 0.671), sleep quality (P = 0.891), or sleep habits (P = 0.951) were observed between NAFLD and non-NAFLD groups in unadjusted analyses. In multivariate logistic regression for the whole cohort, physical exercise was a protective factor (OR = 1.59, 95% CI: 1.11–2.28), while age (OR = 0.97, 95% CI: 0.96–0.99), gender (OR = 0.36, 95% CI: 0.22–0.60), BMI (OR = 0.61, 95% CI: 0.57–0.66), and FPG (OR = 0.63, 95% CI: 0.48–0.81) were significant risk factors (all P < 0.05). Sleep duration, quality, and habits showed no association with NAFLD in the whole cohort. In sex-stratified analyses, men with long sleep duration had a significantly lower risk of NAFLD compared to those with too short sleep duration after adjustment for age, exercise, FPG, and BMI (OR = 0.01, 95% CI: 0.001–0.27, P = 0.032). The trend across sleep duration categories in men was significant only in the fully adjusted model (P trend = 0.032). No significant associations between sleep duration, sleep quality, and NAFLD were found in women across any of the four adjusted models.
**Clinical Implications:** This study suggests that short sleep duration may be an independent risk factor for NAFLD in men but not in women, indicating that sex-specific approaches may be warranted when evaluating sleep-related NAFLD risk. Men with short sleep duration should be counseled about their higher probability of having NAFLD. However, the cross-sectional design precludes causal inference, and the subjective nature of PSQI assessment is a limitation. The findings add to the controversial literature on sleep and NAFLD, with results differing from some prior studies that found associations in both sexes or with poor sleep quality. Larger prospective studies using objective sleep measures (e.g., polysomnography) and accounting for nutritional factors, genetic background, and gut microbiota are needed to clarify these relationships and inform clinical recommendations.