A recent genetic study led by researchers at UCL (University College London) has uncovered a complex relationship between insufficient sleep and the development of depressive symptoms.
Traditionally, poor sleep has been viewed as a consequence of mental health issues, but this study suggests a bidirectional link between sleep and mental well-being.
Published in the journal Translational Psychiatry, the study focused on individuals with an average age of 65 and explored the connection between short sleep duration and the onset of depressive symptoms.
Lead author Odessa S. Hamilton, affiliated with UCL Institute of Epidemiology & Health Care, explained, “The interplay between suboptimal sleep duration and depression is often debated—whether one leads to the other is not clear.
By using genetic predisposition to disease, we determined that it is likely that inadequate sleep precedes the development of depressive symptoms, rather than the other way around.”
Methodology
The researchers analyzed data from 7,146 participants enrolled in the English Longitudinal Study of Ageing (ELSA), a nationally representative population study in England.
They employed genetic and health data to investigate the relationship between sleep duration and the emergence of depressive symptoms over a span of 4–12 years.
Genetic Predisposition and Findings
The study revealed that individuals with a stronger genetic predisposition to short sleep duration (less than five hours per night) were at a higher risk of developing depressive symptoms over time.
Intriguingly, those with a greater genetic susceptibility to depression did not show an increased likelihood of experiencing short sleep.
Dr. Olesya Ajnakina, a senior author of the study, said, “Sleep duration and depression, along with their genetic underpinnings, play significant roles in public health.
Polygenic scores, which reflect an individual’s genetic inclination toward a particular trait, are instrumental in advancing our understanding of the relationship between sleep duration and depressive symptoms.”
Non-Genetic Associations
To bolster their findings, the research team also examined non-genetic associations between depressive symptoms and sleep duration.
They discovered that individuals who slept five hours or less were 2.5 times more likely to develop depressive symptoms.
Conversely, those with depressive symptoms had a one-third higher chance of experiencing short sleep.
The researchers accounted for various factors that could influence the results, including education, wealth, smoking habits, physical activity, and long-standing illnesses.
The study also identified a connection between longer sleep durations and the emergence of depressive symptoms.
Participants who slept more than nine hours were 1.5 times more likely to develop depressive symptoms than those who slept an average of seven hours.
However, depressive symptoms were not linked to extended sleep four to twelve years later, consistent with the genetic findings.
The study’s findings hold important implications for understanding the complex relationship between sleep and depression, particularly as both issues tend to increase with age.
As the global population ages, there is a growing need to delve deeper into the mechanisms connecting these two factors.
Overall, the participants in the study averaged seven hours of sleep per night. At the study’s onset, over 10% slept less than five hours per night, a figure that rose to over 15% by the end of the study period.
The proportion of participants classified as having depressive symptoms increased by approximately 3 percentage points during the study period, from 8.75% to 11.47%.
Both sleep duration and depression have a hereditary component, with previous twin studies suggesting that depression is approximately 35% heritable, and genetic differences accounting for 40% of the variance in sleep duration.
The study combined data on sleep and depressive symptoms from two ELSA surveys conducted two years apart, recognizing that both sleep duration and depression can vary over time.
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The research findings can be found in Translational Psychiatry.
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