Researchers in the UK and USA have shed new light on the internal body clocks that operate our biological schedules. The body clock, also known as the circadian rhythm, is responsible for releasing molecules that signal the body that it is time sleep in the evening and wake up in the morning. New research suggests that some genes may predispose a person to a be morning person -- or conversely a night owl. The authors also identified associations between waking up early and greater psychological well-being and a lower risk of mental disorders, such as schizophrenia and depression.
The study involved 250,000 American participants, whose genomes were analyzed by private company 23andMe, and 450,000 participants who were part of the UK Biobank study. All participants had previously completed a questionnaire that assessed whether they're a "morning person" or an "evening person". Their self-reported sleep-wake routines were confirmed with wrist-worn activity trackers that were used by 85,000 of the UK Biobank participants.
By looking at which genes were common among people who shared sleeping patterns, the researchers found hundreds of new genetic loci (regions), increasing the tally from 24 previously known loci to 351. These include genes that are known to play an important role in our body clocks, as well as genes expressed in the brain and in the retinal tissue in the eye.
“This study highlights a large number of genes which can be studied in more detail to work out how different people can have different body clocks. The large number of people in our study means we have provided the strongest evidence to date that ‘night owls’ are at higher risk of mental health problems, such as schizophrenia and lower mental well-being, although further studies are needed to fully understand this link," Professor Mike Weedon, of the University of Exeter Medical School, who led the research, said in a statement.
The authors say that the retinal tissue connection may explain how the circadian rhythm resets each day in order to align itself with a 24-hour cycle. We use our eyes to make sense of our environment and navigate our surroundings, but sight isn't all that they do. A previous study showed that photosensitive retinal ganglion cells present in the retina -- the most complex part of the eye -- act as sort of light meter, informing the body what time of the day it is. When humans aren't exposed to light our circadian rhythms last longer than 24 hours leading to all sort of health problems.
According to the present work published in Nature, the newly identified gene variants could shift a person's natural waking time by up to 25 minutes. These genetic regions influence the timing of sleep, but not its quality or duration.
However, lifestyle factors such diet, exposure to artificial light, and our jobs seem to play a more important role than genes. The fact remains, though, that if some people are truly predisposed to be night owls, then every little thing can add up to produce significant effects. And all of this could be important since the authors claim that people who stay up at night are more predisposed to mental health conditions such as schizophrenia and depression.
“We know that there are links between how the body clock functions and our health and wellbeing but, to date, we have understood little about the part genetics plays. Now, with the help of publicly funded datasets like UK Biobank, researchers are able to study on an unprecedented scale, the interplay between the genetics of the body clock and the risk of mental health conditions such as schizophrenia and depression. This study provides valuable new insights which we hope will lead to more effective interventions for those most at risk," Dr. Rachael Panizzo, Programme Manager for Mental Health and Addiction at the Medical Research Council, said in a statement.
“By understanding the genetics of sleep and activity timing in the general population, we also gain insights into potential avenues of therapy for individuals with more extreme conditions, such as those with advanced or delayed circadian rhythm disorders," Co-lead author Dr. Jacqueline M Lane, of the Massachusetts General Hospital Department of Anesthesia, added.