Detaching From the Nine-to-Five: How Retirement and Genetics Are Related to Chronotype.

Our sleep-wake rhythm is determined by the interaction of our work-life balance, that is, the 'social clock', and our biological clock. After retirement, the social restrictions generally loosen up, possibly giving more room for our genetic predispositions to regulate the sleep-wake rhythm. In this study, we investigated shifts in wake-up times and chronotypes during employment and retirement. We used data from 20,189 participants from the Netherlands Twin Register. We applied a mixed-effects model to test whether the type of day (working day or non-working day) is a predictor of wake-up time in early birds and late risers. Next, we performed a regression to assess the prevalence of chronotypes in employees and retirees. Then, we tested whether the two groups differed in their wake-up times on working days and non-working days using quantile regression. Finally, we used polygenic scores for morningness to predict the variance in chronotype in employees and retirees. Both early and late risers have later wake-up times on non-working days compared to working days. Employment status was not a predictor of chronotype, but rather of wake-up time on working days. The effect of the polygenic score for morningness on chronotype did not depend on employment status. Our study showed that the social clock influences wake-up time on working days, but not chronotype, making chronotype a relatively stable trait. Additionally, the social clock does not suppress the genetic predisposition for chronotype. These analyses enhance our understanding of how both society and genetics influence our chronotype and sleep-wake rhythm.