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Inconsistent sleep schedule harms metabolic health in middle-aged women
Frequent changes in sleep timing may contribute to higher insulin resistance among nonshift-working, midlife women, according to study findings.
“Irregular sleep schedules, including highly variable bedtimes and staying up much later than usual, are associated in midlife women with insulin resistance, which is an important indicator of metabolic health, including diabetes risk,” Martica H. Hall, PhD, professor of psychiatry at the University of Pittsburgh, said in a press release. “We found that weekday-weekend differences in bedtime were especially important.”
Hall and colleagues evaluated data from the SWAN sleep study on 370 nonshift-working women aged 48 to 58 years to determine whether shifts in sleep timing affects metabolic health. Four areas of sleep timing were measured: mean bedtime, variability in bedtime, bedtime delay and bedtime advance.
After adjustment for race, menopausal symptoms, sleep duration, exercise, depressive symptoms and BMI, positive associations were found between homeostasis model of assessment for insulin resistance (HOMA-IR) and variability in bedtime (P = .007) and bedtime delay (P = .013). Before adjustment, higher HOMA-IR was associated with greater bedtime advance (P = .05). No relationship was found between HOMA-IR and mean bedtime. Higher BMI was linked to greater bedtime advance (P = .047).
“The results are important because diabetes risk increases in midlife women,” Hall said in the release. “Our study suggests that irregular sleep schedules may be an important piece of this puzzle. The good news is that sleep timing is a modifiable behavior. Metabolic health was better in women who had more regular sleep schedules, including regular bedtimes across weekdays and weekends.”
In an accompanying editorial, Joshua J. Gooley, PhD, of Duke-NUS Graduate Medical School in Singapore, wrote that the findings “suggest that moderate variation in sleep timing can potentially influence metabolic health outcomes, but the underlying mechanisms remain to be elucidated.” – by Amber Cox
Disclosure: Gooley and Hall report no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.
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Short sleep duration and poor sleep quality have deleterious health consequences. Accumulative evidence suggests that sleep timing is another important factor to consider. For instance, rotating-shift workers are more likely to develop diabetes relative to non-shift workers, and laboratory studies have shown that acute shifts in sleep timing impair glucose metabolism. This study by Taylor and colleagues extends this literature and shows that habitual shifts in sleep timing, even among non-shift workers, may also affect metabolic health. In a large sample of multiethnic, middle-aged, non-shift working women, the authors report that women with greater day-to-day variability in their bedtime were more likely to have greater insulin resistance relative to women with less variability. In addition, the direction of bedtime shifts might have different effects: Greater advances in bedtime associated with greater BMI. Greater delays in bedtime associated not only with greater insulin resistance at baseline, but also to increased insulin resistance several years later, which suggests that such shifts in bedtime might impair glucose metabolism. These novel findings highlight the need for researchers to further examine the health correlates of sleep timing. Sleep behaviors are complex but modifiable. Understanding if and how variability in sleep timing affects metabolic health could provide rationale for integrating sleep and circadian-related interventions in the treatment and prevention of diabetes, obesity and other metabolic diseases.