Sleep and Cancer Incidence in Alberta's Tomorrow Project Cohort

We aimed to investigate the association between self-reported sleep duration and sleep timing midpoint with all- and site-specific cancer incidence in Alberta's Tomorrow Project (ATP) cohort. Methods: The analysis for sleep duration included 46,300 Albertans aged 35–65 years at baseline from the ATP cohort recruited from 2001–2015. Sleep timing midpoint (wake-time – 1/2 sleep duration) was assessed in a subset of ATP participants (n = 19,820). Cancer incidence was determined through record linkage with the Alberta Cancer Registry in December 2016. Cox proportional hazard regression models evaluated the effects of sleep duration and sleep timing midpoint categories on all- and site-specific (breast, colorectal, lung, prostate, endometrial and hematologic) cancer incidence. Models were adjusted for age, sex (non sex-specific cancers), highest level of education, total household income, marital status, alcohol intake, smoking status, body mass index, family history of cancer, presence of at least one medical condition/co-morbidity, menopausal status (female cancers only) and sleep duration (sleep timing midpoint analysis only). Results: By 2016, there were 3,034 incident cases of cancer in this cohort. A statistical trend was noted for an increased risk of all cancers in participants reporting > 9 hours of sleep/night compared to 7–9 hours of sleep/night (hazard ratio (HR) = 1.16, 95% confidence interval (CI): 0.98–1.36; P = 0.08). Reporting > 9 hours of sleep/night compared to 7–9 hours of sleep/night was also associated with an increased incidence of endometrial cancer (HR = 2.09, 95% CI: 1.16–3.76; P = 0.01). A later sleep timing midpoint (>4:08 AM) versus an intermediate sleep timing midpoint (3:47 AM–4:08 AM) was associated with an increased risk of all (HR = 1.19, 95% CI: 1.03–1.37; P = 0.02) and breast (HR = 1.64, 95% CI: 1.18–2.26; P = 0.003) cancer incidence. Conclusions: These novel findings provide evidence regarding the important role of sleep in cancer etiology. Interventions that put emphasis on proper sleep hygiene for cancer prevention are needed.

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