Certain individuals may be genetically predisposed to being a night owl, according to a recent study published in the journal Sleep. A predisposition to the “eveningness” chronotype may protect against the health problems typically associated with shift work.
Owls and larks
For some, the idea of sleeping anytime other than at night is entirely unthinkable. For others, it is the norm – around a quarter of UK public sector workers regularly work nightshifts. It has long been known that shift workers are predisposed to a wide range of health problems such as cancer and heart disease, often as a result of disruption of the circadian clock. Even when these shift workers finally do get some rest, it is widely reported that they ultimately get less sleep than their 9-5 counterparts.
But if an unconventional sleeping pattern is so dangerous, why do so-called “night owls” exist? Many individuals have what is known as the “eveningness” chronotype – that is, an inherent inclination to stay awake at night. Previous work has shown that those who self-report the eveningness chronotype adapt to nightshift work more easily and are less likely to suffer long-term health problems as a result. In the current study, led by the University of Oxford, the researchers investigated whether eveningness is the result of a genetic predisposition, and the mitigating effect this may have on shift work.
Getting your beauty sleep
Using data from the UK Biobank, the team analysed the genomes of over 53,000 working adults for whom employment data was available. This information included self-reported responses as to whether or not the individual worked nightshifts. The group was categorised based on whether they never, rarely, sometimes, usually or always work at night. Those who always work nightshifts reported an average loss of 13 minutes of sleep per night compared to those who rarely or never work these hours. This cumulative loss of sleep each night is a significant reason that nightshift workers are prone to health issues.
Next, the team assigned a polygenic score to each individual for eveningness, based on the result to a survey question about whether they were a morning or evening person. Using these scores, the team then analysed whether a genetic predisposition to being a night owl mitigated the effect of nightshift work. They observed that, in those who always worked these unconventional hours, the sleep penalties were significantly reduced if the individual also displayed a strong genetic predisposition to eveningness. For each standard deviation increase in the eveningness score, an average of four minutes of additional sleep was gained.
Minimising the impact
With so many individuals carrying out essential night shift work, it is crucial to find ways to mitigate the health effects. For example, in one recent study, it was suggested that shift workers could engage in time-restricted eating to minimise circadian dysregulation. The current study confirms that, whilst nightshift workers typically face an accumulation of sleep penalties, those predisposed to being a night owl are protected to an extent, suggesting that there is no one size fits all approach to handling shift work. Senior author Professor Melinda Mills stated: “There are health implications for night shift workers, but our study shows that these vary between individuals dependent on their chronotype, and that should be considered when designing interventions.”