Irregular Sleep Schedule Linked With Depression, Worse Mood

Early-career physicians with an irregular sleep schedule were found to be at an increased risk for depression over the long term, with short-term consequences shown to affect mood the next day, according to study findings published in npj Digital Medicine.

Although several factors play a distinct role in evaluating sleep health, the researchers highlight that studies often focus solely on sleep duration in their analyses. Moreover, 24-hour total sleep time (TST), an established critical driver of major depression, remains poorly understood due to reliance “on either self-report assessments or traditional objective sleep measurements restricted to cross-sectional time frames and small cohorts.”

Seeking to build on emerging evidence that has identified the sleep-wake schedule as a particularly important and stable contributor to health over time, they assessed 2115 early-career physicians (mean [SD] age, 27.5 [2.4] years; 56% female) who were all in their first year of residency training after medical school. Participants were analyzed in the 2 weeks prior to the study and then for 1 year during residency, which was characterized by long, intense work days and irregular work schedules that contributed to day-to-day variance in sleep.

Through the study, the authors aimed to:

• Delineate the changes in objective, longitudinally monitored sleep with the transition into internship
• Identify the specific objective sleep characteristics, including variability, associated with depression over the course of the intern year
• Evaluate the impact of day-to-day changes in objective sleep duration and sleep-wake timing on mood the next day

They evaluated sleep via wearable device, daily mood with a smartphone application, and depression through the 9-item Patient Health Questionnaire (PHQ-9).

"The advanced wearable technology allows us to study the behavioral and physiological factors of mental health, including sleep, at a much larger scale and more accurately than before, opening up an exciting field for us to explore," said lead study author Yu Fang, MSE, research specialist at the Michigan Neuroscience Institute, in a statement. "Our findings aim not only to guide self-management on sleep habits but also to inform institutional scheduling structures."

Among the study cohort, several factors were associated with more depressive symptoms:

• Reduced TST (b = −0.11; P < .001)
• Later bedtime (b = 0.068; P = .015)
• Increased variability in TST (b = 0.4; P = .0012)
• Wake time (b = 0.081; P = .005).

In comparing the aggregated impact of sleep variability and mean sleep parameters, both were found to be similar in magnitude on PHQ-9 scores (both: r², 0.01).

Furthermore, after evaluating objective sleep duration and sleep-wake timing on mood the next day, improved next-day mood was associated with:

• Later wake time (b = 0.09; P  < .001) and earlier bedtime (b = −0.07; P < .001)
• Increased TST (b = 0.06; P  < .001) and lower day-to-day shifts in TST (b, −0.011; P < .001)
• Wake time (b = −0.004; P < .001)

“Variability in sleep parameters substantially impacted mood and depression, similar in magnitude to the mean levels of sleep parameters,” concluded the study authors. “Interventions that target sleep consistency, along with sleep duration, hold promise to improve mental health.”

Due to the young patient cohort, authors note that study findings are not representative of the general population.

Reference

Fang Y, Forger DB, Frank E, Sen S, Goldstein C. Day-to-day variability in sleep parameters and depression risk: a prospective cohort study of training physicians. NPJ Digit Med. Published online February 18, 2021. doi:10.1038/s41746-021-00400-z