Summary: A large genomic study finds that people genetically predisposed to be morning types tend to have better mental health and a lower risk of psychiatric disorders such as schizophrenia and depression. The study also identifies many new genetic regions linked to sleep timing, highlights the eye’s role in synchronizing the body clock, and finds no strong genetic connection between chronotype and metabolic conditions like obesity or diabetes.
Source: University of Exeter.
Large-scale genomic analysis clarifies how the body clock connects to mental health and disease
A comprehensive genetic study, published in Nature Communications, reveals new details about the human body clock and its relationship to mental health. The analysis suggests that individuals genetically inclined to be early risers generally report better overall well-being and carry a reduced risk of psychiatric conditions such as schizophrenia and depression. Contrary to some earlier reports, the researchers did not find strong genetic links between chronotype (morningness or eveningness) and metabolic diseases like obesity or type 2 diabetes.
The international research team, led by the University of Exeter in collaboration with Massachusetts General Hospital and funded by the Medical Research Council, examined genetic data from hundreds of thousands of participants. Their findings increase the number of genetic regions associated with being a “morning person” from 24 to 351, offering many new targets for further study into how individual body clocks vary.
Professor Mike Weedon of the University of Exeter Medical School, who led the project, noted that the study identifies numerous genes that deserve deeper investigation to explain why people differ in their circadian timing. He said the large sample size provides the strongest evidence to date linking evening preference with higher risk of mental health issues, though further research is needed to fully understand the causal pathways.
The analysis combined self-reported chronotype information from roughly 250,000 participants in a US-based dataset provided by a private genomics company and 450,000 participants from the UK Biobank. Participants answered whether they considered themselves a “morning person” or an “evening person,” and researchers scanned their genomes for shared variants associated with sleep timing.
To validate their genetic results, the team used wrist-worn activity monitor data from more than 85,000 UK Biobank participants. These objective activity measures confirmed that the identified genetic variants shift an individual’s natural wake time by up to about 25 minutes on average — for example, moving a typical wake time from 8:00 a.m. to around 8:25 a.m. The study found these variants affected the timing of sleep rather than sleep duration or quality.
The genetic regions implicated by the study include core circadian clock genes as well as genes active in the brain and retinal tissue of the eye. Because the human circadian cycle is slightly longer than 24 hours, signals from the retina help the brain detect light and reset the internal clock daily, aligning physiological rhythms with the day-night cycle. The new results reinforce the retina’s functional role in synchronizing circadian timing with environmental light.
Body clocks are shaped by both genetic factors and lifestyle influences such as diet, light exposure, work schedules and daily activities. Circadian rhythms regulate many molecular processes, including hormone secretion, core body temperature, alertness and the timing of sleep and wakefulness. Small genetic differences in how the brain and retina respond to light can modestly alter internal timing and, according to this study, may meaningfully influence mental health risk.
Lead author Dr. Samuel E. Jones of the University of Exeter Medical School emphasized that while fundamental clock mechanisms in the brain were recognized with the 2017 Nobel Prize in Physiology or Medicine, much remains unknown about how circadian variation affects disease risk. “Our work indicates that differences in both brain responses to external light and the intrinsic function of internal clocks help explain why some people are morning types while others are night owls,” he said. “These subtle differences in timing can potentially affect susceptibility to mental health disorders.”
Co-lead author Dr. Jacqueline M. Lane of the Massachusetts General Hospital Department of Anesthesia added that mapping the genetics of sleep and activity timing in the general population provides a foundation for developing therapies for more extreme circadian disorders, such as advanced or delayed sleep phase syndromes.
Dr. Rachael Panizzo, Programme Manager for Mental Health and Addiction at the Medical Research Council, said the study demonstrates how large, publicly funded datasets make it possible to explore the genetic links between circadian timing and mental health at an unprecedented scale. She noted the research offers new insights that could lead to better interventions for people most at risk of psychiatric conditions.
Dr. Dave Hinds, Principal Scientist for Statistical Genetics at 23andMe, commented that participant-contributed data enabled the study and that genetic reports identifying morning or evening predisposition are now available to customers. He said the results improve estimates of the genetic contribution to chronotype and help clarify how one facet of sleep behavior relates to broader health outcomes.
Source: Louise Vennells – University of Exeter
Publisher: NeuroscienceNews.com (reporting organized by the publisher)
Image Source: Public domain image provided to NeuroscienceNews.com.
Original Research: The study appears in Nature Communications.