Genetic variation influences whether someone is a morning person, with potential consequences for mental health, reports a paper published in Nature Communications this week. This large-scale genome-wide association study expands on previous work and increases the total number of genetic loci that may be associated with chronotype (the innate propensity to sleep at a particular time) from 24 to 351.
Michael Weedon and colleagues analysed genetic variation in two populations totalling 697,828 participants for an association with self-reported morningness. Of the loci identified in this analysis, 327 had not been associated with chronotype previously. As self-reporting can be inaccurate or biased, the authors sought further validation for these findings using data from a subset of participants (85,760) for whom objective measures of sleep were available via the use of an activity monitor. The results confirmed that the chronotype loci are associated with sleep timing, but not the quality or duration. Using multiple statistical tests to study the relationship between chronotype and disease, they found that being a morning person was correlated with higher subjective well-being and was also associated with a lower risk of depression and schizophrenia.
The authors note that the majority of findings are based on self-reporting (i.e. questionnaire responses), which might be prone to reporting bias, and that further studies are required to confirm any causal role these genetic variants may play in the risk of developing diseases.