Are you a night owl or a morning lark? The answer is influenced by at least 351 regions of the genome, a recent study has found.
Whether someone is a morning person or an evening person – a trait known as a 'chronotype' – was previously known to be influenced by 24 genes (see BioNews 838). The new study compared genomic data with the participants' self-reported accounts of sleep habits, to reveal hundreds of genes newly associated with chronotype.
'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,' said Dr Mike Weedon from the University of Exeter Medical School, who led the international collaboration.
The study, published in Nature Communications, analysed the genomes of nearly 700,000 people, using data from the personal genomics company 23andMe and the UK Biobank. Because self-reported measures of chronotype can be unreliable, the researchers confirmed the findings using from wristband activity monitors worn by around 85,000 individuals in the UK Biobank. This established that morning people wake up around half an hour earlier than night owls.
'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,' said Dr Weedon.
One possible explanation for the link with mental health is the 'social jetlag' suffered by night owls. 'Morning people are better aligned with a 9-to-5-type society,' Dr Weedon told CNN. 'The new biology we've helped uncover may lead to treatments for conditions caused by a disruption of body clocks.'
Previous research had found a link between chronotype – specifically being a night owl – and a greater risk of diabetes and obesity. However, the new study did not find that the genes discovered contributed directly to diabetes or obesity.
The regions of the genome found to be relevant to chronotype included genes involved in metabolism and the biological clock, as well as genes that function in the retina – where daily light fluctuations help 'entrain' the body clock.
'This may suggest that the retinas of owls are less effective at detecting and communicating light levels, resulting in poorer entrainment of the clock,' wrote study co-author Dr Samuel Jones at the University of Exeter, in an article for The Conversation.
The researchers have said that their future studies will turn to the genetics of sleep duration and disorders such as insomnia.