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/m2. 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.

Distinct Time Course of the Decrease in Hepatic AMP-Activated Protein Kinase and Akt Phosphorylation in Mice Fed a High Fat Diet.

AMP-activated protein kinase (AMPK) plays an important role in insulin resistance, which is characterized by the impairment of the insulin-Akt signaling pathway. However, the time course of the decrease in AMPK and Akt phosphorylation in the liver during the development of obesity and insulin resistance caused by feeding a high fat diet (HFD) remains controversial. Moreover, it is unclear whether the impairment of AMPK and Akt signaling pathways is reversible when changing from a HFD to a standard diet (SD). Male ddY mice were fed the SD or HFD for 3 to 28 days, or fed the HFD for 14 days, followed by the SD for 14 days. We examined the time course of the expression and phosphorylation levels of AMPK and Akt in the liver by immunoblotting. After 3 days of feeding on the HFD, mice gained body weight, resulting in an increased oil red O staining, indicative of hepatic lipid accumulation, and significantly decreased AMPK phosphorylation, in comparison with mice fed the SD. After 14 days on the HFD, systemic insulin resistance occurred and Akt phosphorylation significantly decreased. Subsequently, a change from the HFD to SD for 3 days, after 14 days on the HFD, ameliorated the impairment of AMPK and Akt phosphorylation and systemic insulin resistance. Our findings indicate that AMPK phosphorylation decreases early upon feeding a HFD and emphasizes the importance of prompt lifestyle modification for decreasing the risk of developing diabetes.