Sleep disruption, chronotype, shift work, and prostate cancer risk and mortality: a 30-year prospective cohort study of Finnish twins: Beyond the Abstract

In a large, prospective study, we found a significant association between chronotype and total prostate cancer risk. Chronotype, or diurnal preference, is characterized by an individual’s preference for morning or evening activity. “Somewhat evening” types were at a 30% higher risk compared to “definite morning” types. Further, chronotype significantly modified the relationship between shift work and prostate cancer risk. We found no association between sleep duration, sleep quality, or shift work and risk. 

This study was conducted in a large population of Finnish twins with 30 years of follow-up data and linkage to national registries. This unique population allowed us to also examine associations within twin pairs, thereby controlling for potentially confounding genetic and shared early environmental factors. Our co-twin analyses did not detect an association for any of the circadian- or sleep-related factors under study. This may have been a chance finding due to lower power of the discordant twin pair analysis, or it may suggest that the significant association between chronotype and risk in the overall study population was driven by an unaccounted for shared genetic or environmental confounder.

Shift work may increase prostate cancer risk through mechanisms of sleep disruption, circadian disruption, and/or light-induced suppression of melatonin secretion. Recent evidence suggests that chronotype may influence adaptability to various work schedules and thereby act as a unique marker of susceptibility to sleep and circadian disruption. Our findings highlight the importance of looking beyond cancer risk associated with working in a particular time window to a more personalized examination of the risk associated with working in a time window that is not compatible with one’s diurnal preference.

Written by: Barbra Dickerman 

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