Chronotype, sleep timing, sleep regularity, and cancer risk: A systematic review.

Sleep is a multidimensional modifiable lifestyle factor related to cancer risk. Prior research has primarily focused on sleep duration, despite the increasing importance of sleep timing and sleep regularity in the health research field. The objective of this systematic review was to synthesize the existing literature on the relationship of chronotype, sleep timing, and sleep regularity with cancer risk. We searched four databases (PubMed, CINAHL, PsychInfo, and Embase) in October 2024. The sleep exposures of interest included sleep timing, sleep regularity, sleep midpoint, social jetlag, chronotype, and weekend catch-up sleep, and the outcome of interest was cancer incidence (overall or site-specific). A total of 22 studies were included, of which 18 investigated chronotype, two investigated social jetlag, two investigated sleep midpoint, and one investigated weekend catch-up sleep as the sleep exposure. The majority of studies assessed sleep using self-reported questionnaires (95%) and investigated site-specific cancer incidence (91%). We found no consistent evidence linking late chronotype, later sleep midpoint, increased social jetlag, or weekend catch-up sleep to elevated risk of cancer. This review highlights the heterogeneity in how sleep timing and sleep regularity are assessed. Future research should standardize measures on how to quantify sleep timing and sleep regularity and replication studies in diverse populations are needed. Current evidence on linking sleep timing, sleep regularity, and chronotype with cancer risk remains inconclusive.