The scientists found that having one of 15 genetic variants increased a person's chances of being a morning person by between 5 percent and 25 percent, according to the study. Women were more likely to be early risers (48.4 percent, compared with 39.7 percent of men). And people over 60 said they preferred mornings more than those under 30 (63.1 percent, compared with 24.2 percent of participants under age 30), the researchers said.
The researchers used the fruit-fly Drosophila to identify the genes associated with morningness and eveningness. The research focused on the timing of adult emergence (eclosion) from their pupal case, an event which is regulated by the circadian clock. While most strains exhibit eclosion during dawn ('larks'), the team surveyed large number of wild strains and identified strains that exhibit late eclosion ('owls'). The team used a method called RNA sequencing (RNA-seq) to quantify gene expression across an entire genome. By comparing gene expression in 'lark' and owl strains, the team has identified nearly 80 genes that show substantial difference in their expression and may account for the different diurnal preference.
The researchers noted no significant differences in age, body mass, or metabolic syndrome between the groups. However, they did find differences in how energy sources were used by those with early and late chronotypes.
Most of us have some degree of preference for late nights or early mornings. Where an individual falls on this spectrum largely determines his or her chronotype -- an individual disposition toward the timing of daily periods of activity and rest. Some of us are clearly "larks" -- early risers -- while others of us are distinctly night owls. The rest of us fall somewhere in between the two.
New research has now found evidence of physical differences in the brains of different chronotypes. Scientists at Germany's Aachen University conducted brain scans of early risers, night owls, and "intermediate" chronotypes who fell in between the two ends of the spectrum. They discovered structural differences in the brains of people with different sleep-wake tendencies. Researchers observed a group of 59 men and women of different chronotypes: 16 were early risers, 20 were intermediate sleepers, and 23 were night owls. They found that compared to early risers and intermediates, night owls showed reduced integrity of white matter in several areas of the brain. White matter is fatty tissue in the brain that facilitates communication among nerve cells. Diminished integrity of the brain's white matter has been linked to depression and to disruptions of normal cognitive function.
The cause of this difference in quality of white matter among night owls compared to other sleepers is not clear. Researchers speculate that the diminished integrity of white matter may be a result of the chronic "social jet lag" that characterizes the effects of the sleep-wake routines of many night owls. People who are disposed toward staying up late and sleeping late often find themselves at constant odds with the schedule of life that surrounds them, particularly work and school schedules that require early-morning starts. This can leave night owls chronically sleep deprived, and experiencing many of the same symptoms -- fatigue and daytime sleeplessness, difficulty focusing, physical pain and discomfort -- of travel-induced jet lag.
This latest study is the first to offer physical evidence of neurological differences among people with different sleep tendencies. But other research has also shown that the inclinations toward staying up late or rising early are deeply rooted in biological and genetic differences:
Research has also revealed differences in brain metabolic function among night owls compared to early risers and middle-of-the-road sleepers. These metabolic differences were discovered in regions of the brain involved in mood, and may be one reason why night owls are at higher risk for depression related to insomnia.
Recently, scientists identified a gene variant that exerts a strong influence over the circadian clock, and with the inclination to stay up late or rise early. This genetic variation -- which affects nearly the entire population -- can shift the timing of an individual's 24-hour sleep-wake cycle by as much as 60 minutes.
The genetic make-up of the circadian timing system underpins the difference between early and late chronotypes, or early birds and night owls. While it has been suggested that circadian rhythms may change over time, including dramatic changes that turn a morning lark to a night owl or vice versa, evidence for familial patterns of early or late waking would seem to contradict this, and individual changes are likely on a smaller scale.
Researchers from the department of genetics at the University of Leicester published a study earlier this month in Frontiers in Neurology that found different fruit flies emerged from their pupal case, or "woke up," at different times of the day. The study authors then found they could replicate the behavior of the late risers through selective breeding, IFLScience reported, indicating a link between sleep behaviors and genetics.
The University of Leicester study shines new light on the reasons for these cycles and, if true, would indicate late risers were not merely "delayed" early risers but in fact working under a completely different operating principle, based at least partially on uncontrollable genetic circumstances.
They say the early bird catches the worm, but night owls may be missing far more than just a tasty snack. Researchers have discovered the first physical evidence of structural brain differences that distinguish early risers from people who like to stay up late. The differences might help to explain why night owls seem to be at greater risk of depression.
The link between the different hierarchies of personality, sleep patterns and even genetics has been discovered by researchers from the Department of Psychology at the University of Warwick.A typical example of a morning person is thought to be someone who wakes up naturally at 6am, goes for a jog, showers, has breakfast and is ready for a productive day at work by 9am. Whereas an evening person struggles to get up in the morning and feels more productive in the evening.Researchers from the University of Warwick with colleagues from the University of Tartu have recently had the paper, 'Personality Traits Relate to Chronotype at Both the Phenotypic and Genetic Level' published in the Journal of Personality, in which they have analysed the relationship between sleep timing (chronotype), preference to the morning/evening, and personality traits at a phenotypic and genetic level.Ultimately the researchers have found that the relationship between personality and morningness-eveningness is partly due to genetic factors.Using a large-scale sample of participants form the Estonian Biobank researchers asked them to answer questionnaires about their sleep timings and personality, personality was also assessed by someone who knew the participant well. Once answered researchers were able to identify the phenotypic relationships between the sleep and personality.However they were also able to calculate the genetic correlations through summary statistics of large genome-wide association studies of personality and sleep preferences.Personalities can be divided into three hierarchies: personality domains, facets and items, researchers analysed all three, but in particular they found on a domain level that people high in Conscientiousness and low in Openness were associated with being earlier chronotypes (i.e., they went to bed and got out of bed earlier).On a facet level, researchers found that less straightforward (a facet of Agreeableness) and excitement-seeking (a facet of Extraversion), yet more self-disciplined (a facet of Conscientiousness) people were more likely to have earlier chronotypes. Higher Conscientiousness and lower Openness were also genetically related to preference for morningness.Postgraduate researcher Dr Anita Lenneis, from the Department of Psychology at the University of Warwick comments:"Our findings have helped us to come up with two possible pathways of how personality might influence chronotype. Personality traits such as Conscientiousness and C5: Self-discipline in particular may influence chronotype through shaping people's preferences for various social activities and behaviours which in turn, may influence what time people go to and get out of bed, or personality may influence chronotype is through active decisions people make regarding their sleep."However, it could also be that chronotype influences personality or that chronotype and personality mutually influence each other. The findings of the genetic correlations support this view but further studies will be necessary to better understand the shared genetic mechanisms between the two constructs as well as the causality of their relationships."Professor Anu Realo, from the Department of Psychology at the University of Warwick adds:"Not only have we shown there is a relationship between chronotype, personality and partially your genes, our findings also suggest that it might be possible to change your chronotype or at least train yourself into a different more socially convenient sleep pattern by increasing your self-control. Ideally work hours would be adapted to your chronotype, but if not, evening people who typically experience worse health could learn to go to bed at earlier hours which might also accelerate the release of melatonin. Melatonin is also influenced by artificial light, so regularly turning off the lights at earlier hours might also lead to falling asleep at earlier hours of the evening. However, future studies will need to investigate whether such interventions to enhance self-control would result in a permanent change or would indeed promote better health in later chronotypes."Reference: Lenneis A, Vainik U, Teder-Laving M, et al. Personality traits relate to chronotype at both the phenotypic and genetic level. J Pers. 2021. doi: 10.1111/jopy.12645This article has been republished from the following materials. Note: material may have been edited for length and content. For further information, please contact the cited source. 2b1af7f3a8