Association between obesity and self-reported sleep duration variability, sleep timing, and age in the Japanese population.

OBJECTIVE

The objective of this study was to investigate the association between obesity and sleep habits, including bedtime, wake-up time, and sleep duration variability over a week.

METHODS

We analyzed 9289 participants in this study. Following a health examination, each participant self-reported their sleep habits using a standardized 19-item questionnaire. High sleep duration variability was defined as sleep varying ≥3h of the difference between the longest and shortest sleep durations reported over a week-long period. Late bedtime and early wake-up time were defined as 24:00h or later, and before 6:00h, respectively. Obesity was defined as a body mass index (BMI) of ≥25kg/m. Subgroup analysis included age (younger group defined as age <65 years vs. elderly group defined as age ≥65 years).

RESULTS

After adjusting for confounding factors and sleep duration, high sleep duration variability [odds ratio (OR), 1.20; p<0.005] was significantly associated with a high OR of obesity. Late bedtime (OR, 1.18; p<0.01) was significantly associated with a high OR of obesity, whereas early wake-up was not. In the subgroup analysis, high sleep duration variability had a significant association with the younger group (OR, 1.25; p<0.001), whereas late bedtime had a significant association with the elderly group (OR, 1.36; p<0.005).

CONCLUSIONS

Inappropriate sleep habits, particularly high sleep duration variability in young individuals and late bedtime in the elderly, are associated with a high prevalence of obesity, independently of sleep duration.