Study: Sleep Schedule Associated With Insulin Resistance

Irregular sleep schedules, including highly variable bedtimes and staying up much later than usual, are associated with insulin resistance in midlife women, according to a new study.

“Insulin resistance is an important indicator of metabolic health, including diabetes risk,” said lead study author Briana J. Taylor, MS, of the department of psychology, University of Pittsburgh. “When we took a closer look at the data, we found that weekday-weekend differences in bedtime were especially important.”
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White (n=161), African-American (n=121), and Chinese (n=56) non-shift-working women 48-58 years old not taking insulin-related medications participated in the Study of Women’s Health Across the Nation Sleep Study. The researchers subsequently examined participants approximately 5.39 (standard deviation=0.71) years later.

They used daily diary-reported bedtimes to calculate four measures of sleep timing  (mean bedtime, bedtime variability, bedtime delay, and bedtime advance) and measured BMI and insulin resistance (homeostatic model assessment-insulin resistance, HOMA-IR) at two time points. Linear regressions evaluated whether sleep timing was associated with BMI and HOMA-IR cross-sectionally and prospectively.

In cross-sectional models, the investigators found greater variability in bedtime and greater bedtime delay associated with higher HOMA-IR (β=0.128; P=0.007, and β=0.110; P=0.013, respectively). Greater bedtime advance also was associated with higher BMI (β=0.095; P=0.047). Prospectively, greater bedtime delay predicted increased HOMA-IR at Time 2 (β=0.152; P=0.003). They said the results were partially explained by shifted sleep timing on weekends.

“Most surprisingly, we found that frequently going to bed earlier than usual during the week was associated with a higher body mass index,” Taylor said. “Together our findings suggest that large deviations in bedtime in either direction (i.e., later or earlier) were associated with worse metabolic health.”

She noted the link between sleep schedules and insulin resistance weren’t explained by the amount of sleep women got at night or by other factors, such as race, menopausal status, physical activity, or symptoms of depression.

“Diabetes risk increases in midlife women, and our study suggests that irregular sleep schedules may be an important piece of this puzzle,” Taylor said. “Metabolic health was better in women who had more regular sleep schedules, including regular bedtimes across weekdays and weekends. Although future research is needed in this area before this work can inform clinical recommendations, primary care providers should acknowledge the significant impact of sleep on health outcomes and be mindful of the sleep behaviors that may contribute to life-altering health outcomes.”

-Mike Bederka

Reference:

Taylor BJ, Matthews KA, Hasler BP, et al. Bedtime variability and metabolic health in midlife women: the SWAN Sleep Study. SLEEP. 2016;39(2):457-465.