The Association between Sleep Duration and Non-Alcoholic Fatty Liver Disease among Japanese Men and Women

OBJECTIVE To examine the relationship between sleep duration and non-alcoholic fatty liver disease (NAFLD). METHODS We evaluated 3,968 subjects who underwent health check-ups from June 2012 to May 2013 at the Watari Hospital Health Center in Fukushima Prefecture in Japan. Fatty liver was detected by ultrasonography. Sleep duration and lifestyle factors were estimated using a questionnaire. Sleep duration was categorized into the following groups: ≤ 6, 6 to ≤ 7, >7 to ≤ 8, and >8 h. The four sleep duration groups were compared using the χ(2) test and Kruskal-Wallis test. RESULTS In total, 2,172 subjects were enrolled. The overall prevalence of NAFLD was 29.6% (men, 38.0%; women, 25.3%). The proportion of NAFLD tended to decrease as sleep duration increased in men. The proportion with NAFLD was lowest in the group with a sleep duration of 6 to ≤ 7 h and highest in the groups with sleep durations of ≤ 6 and >8 h in women. The distribution showed a U-shaped curve. The age-adjusted odds ratio (OR) (95% confidence interval (CI)) for subjects with NAFLD with a sleep duration ≤ 6 h compared to the reference (6 to ≤ 7 h) was 1.44 (1.06-1.96) in women. CONCLUSION Sleep shortage tends to be associated with NAFLD in women and may be mediated by body adiposity.