Association between nighttime sleep duration, midday naps, and glycemic levels in Japanese patients with type 2 diabetes.

OBJECTIVES: To clarify the relationship between nighttime sleep duration, midday naps, and glycemic control in Japanese patients diagnosed with type 2 diabetes (n = 355) or impaired glucose tolerance (n = 43).

METHODS: A total of 398 patients completed a self-administered questionnaire on sleep duration/quality and were divided into five groups according to their self-reported nighttime sleep duration: <5 h, 5-6 h, 6-7 h, 7-8 h, and >8 h. Each group was further divided into two subgroups each according to the presence or absence of midday naps. Poor glycemic control was defined as HbA1c ≥ 7.0%.

RESULTS: Short nighttime sleep (<5 h), poor sleep induction, daytime sleepiness, and low sleep satisfaction were associated with high HbA1c levels. HbA1c was higher in the short nighttime sleep/no nap group than in non-nappers with different nighttime sleep duration, whereas the short nighttime sleep/nap group showed similar HbA1c levels to the other nap subgroups. In multivariate logistic regression models, after adjusting for a number of potential confounders, short (<5 h) nighttime sleep without nap was significantly associated with poor glycemic control compared with 6-7 h nighttime sleep without nap (OR [95% CI]: 7.14 [2.20-23.20]). However, taking naps reduced this risk for poor glycemic control in short sleepers. Other risk factors for poor glycemic control were low sleep satisfaction (1.73 [1.10-2.70]) and poor sleep induction (1.69 [1.14-2.50]).

CONCLUSIONS: Poor sleep quality and quantity could aggravate glycemic control in type 2 diabetes. Midday naps could mitigate the deleterious effects of short nighttime sleep on glycemic control.

CLINICAL TRIALS REGISTRATION: UMIN 000017887.