Sleep plays an important role in cognitive function, such as emotional regulation, which is important for a higher quality of life. The study objective was to explore the association between baseline sleep quality and 6-year incidence of clinical depression. Using data from the Comprehensive cohort of the Canadian Longitudinal Study on Aging from baseline (2011-2015) to follow-up 2 (2018-2021), a total cohort of 13,997 middle aged and older Canadians free of self-reported diagnosis of clinical depression at baseline was obtained wherein the baseline mean age was 66 years (SD = 7.8), 50.3 % were female, 5.7 % were non-white, and 4.3 % had incident depression by follow-up 2. Sleep-related exposures included self-reported sleep quality (ranging from very dissatisfied to very satisfied), sleep duration, sleep frequencies (initiation difficulty, maintenance difficulty, daytime sleepiness), and symptoms of sleep disorders (sleep apnea, acting out dreams while asleep, restless leg syndrome). Multivariable regression models were used to assess the association between self-reported incident clinical depression and each sleep exposure, adjusting for several covariates (age, sex, sociodemographic, and health characteristics). Fully adjusted models demonstrated that individuals who were very dissatisfied with their sleep quality had 1.6 times the odds of reporting new depression while those with satisfied sleep had 1.2 times the odds of reporting new depression, compared to those who reported very satisfied sleep. Those with ≤4 h of sleep and those with 10+ hours of sleep had a higher predicted probability of having depression by 6-year follow-up, compared to those with 7 to 8 hours of sleep. This analysis suggests that poorer sleep quality may be associated with incident clinical depression, supporting the potential benefit of preventative measures and improvements to individuals' sleep in reducing the risk of depression.
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