Changes in sleep and the prevalence of probable insomnia in undergraduate university students over the course of the COVID-19 pandemic: findings from the U-Flourish cohort study.

BACKGROUND: Sleep problems associated with poor mental health and academic outcomes may have been exacerbated by the COVID-19 pandemic. AIMS: To describe sleep in undergraduate students during the COVID-19 pandemic. METHOD: This longitudinal analysis included data from 9523 students over 4 years (2018-2022), associated with different pandemic phases. Students completed a biannual survey assessing risk factors, mental health symptoms and lifestyle, using validated measures. Sleep was assessed with the Sleep Condition Indicator (SCI-8). Propensity weights and multivariable log-binomial regressions were used to compare sleep in four successive first-year cohorts. Linear mixed-effects models were used to examine changes in sleep over academic semesters and years. RESULTS: There was an overall decrease in average SCI-8 scores, indicating worsening sleep across academic years (average change -0.42 per year; P-trend < 0.001), and an increase in probable insomnia at university entry (range 18.1-29.7%; P-trend < 0.001) before and up to the peak of the pandemic. Sleep improved somewhat in autumn 2021, when restrictions loosened. Students commonly reported daytime sleep problems, including mood, energy, relationships (36-48%) and concentration, productivity, and daytime sleepiness (54-66%). There was a consistent pattern of worsening sleep over the academic year. Probable insomnia was associated with increased cannabis use and passive screen time, and reduced recreation and exercise. CONCLUSIONS: Sleep difficulties are common and persistent in students, were amplified by the pandemic and worsen over the academic year. Given the importance of sleep for well-being and academic success, a preventive focus on sleep hygiene, healthy lifestyle and low-intensity sleep interventions seems justified.