A recent genetic study led by researchers from UCL (University College London) suggests that consistently sleeping less than five hours a night may increase the likelihood of developing depressive symptoms. Traditionally, poor sleep has been viewed as a consequence of mental health issues, but this study reveals a more intricate relationship between sleep and mental well-being.

Published in the journal Translational Psychiatry, the study examined data from individuals with an average age of 65 and found that insufficient sleep was linked to the emergence of depressive symptoms.

Lead author Odessa S. Hamilton (UCL Institute of Epidemiology & Health Care) stated, “We face a dilemma regarding whether suboptimal sleep duration precedes or follows depression. While they often co-occur, the primary sequence has been largely unresolved. By employing genetic susceptibility to disease, we concluded that sleep likely precedes the onset of depressive symptoms, rather than the other way around.”

The researchers analyzed genetic and health information from 7,146 participants enrolled in the English Longitudinal Study of Ageing (ELSA), a nationally representative population study in England.

They discovered that individuals with a higher genetic predisposition to short sleep (less than five hours per night) were more likely to experience depressive symptoms over a span of 4-12 years. However, those with a greater genetic predisposition to depression did not show an increased likelihood of experiencing short sleep.

Senior author Dr. Olesya Ajnakina (UCL Institute of Epidemiology & Health Care and the Institute of Psychiatry, Psychology & Neuroscience at King’s College London) explained, “Both short and long sleep durations, as well as depression, are significant contributors to the public health burden and have a strong hereditary component. Polygenic scores, which reflect an individual’s genetic propensity for a trait, are believed to be pivotal in gaining insight into the relationship between sleep duration and depressive symptoms.”

The researchers evaluated the strength of genetic predisposition among the ELSA participants using data from previous genome-wide association studies that identified numerous genetic variations associated with a heightened likelihood of developing depression and experiencing short or long sleep.

In addition to genetic associations, the research team investigated non-genetic connections between depressive symptoms and sleep duration. They found that individuals sleeping five hours or less were 2.5 times more likely to develop depressive symptoms, while those with depressive symptoms were about a third more likely to experience short sleep. The researchers adjusted for various factors that could influence the results, including education, wealth, smoking habits, physical activity, and chronic illnesses.

The study also revealed a correlation between prolonged sleep and the development of depressive symptoms, with participants sleeping more than nine hours being 1.5 times more likely to experience depressive symptoms than those who slept an average of seven hours. However, depressive symptoms were not associated with extended sleep duration four to 12 years later, aligning with the genetic findings.

Professor Andrew Steptoe (Head of Behavioural Science and Health, UCL Institute of Epidemiology & Health Care) commented, “Suboptimal sleep and depression increase with age, and with the worldwide phenomenon of population ageing there is a growing need to better understand the mechanism connecting depression and a lack of sleep. This study lays important groundwork for future investigations on the intersection of genetics, sleep, and depressive symptoms.”

On average, the participants in the study slept for seven hours per night. At the beginning of the study period, over 10% slept for less than five hours a night, which increased to over 15% by the end of the study period. The percentage of participants classified as having depressive symptoms rose by approximately 3 percentage points, from 8.75% to 11.47%.

Both sleep duration and depression have a hereditary component, with earlier twin studies suggesting that depression is approximately 35% heritable, and genetic differences account for 40% of the variation in sleep duration. In this study, data on sleep and depressive symptoms were combined from two ELSA surveys conducted two years apart, recognizing that sleep duration and depression can fluctuate over time.

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