A recent study conducted by researchers at UCL (University College London) has revealed a link between consistently sleeping less than five hours per night and an increased risk of developing depressive symptoms. The study challenges the notion that poor sleep is simply a consequence of mental illness and suggests that sleep duration may actually precede the onset of depression.
The researchers analyzed genetic data from 7,146 individuals and found that those with a genetic predisposition to shorter sleep were more susceptible to developing depressive symptoms. Interestingly, a genetic inclination for depression did not increase the likelihood of shorter sleep duration.
Individuals who consistently slept five hours or less per night were 2.5 times more likely to exhibit depressive symptoms compared to those who slept longer. However, individuals with depressive symptoms had only a one-third increased chance of experiencing short sleep. This suggests that sleep duration and depression both have a hereditary component, with twin studies indicating a 35% heritability for depression and a 40% heritability for variations in sleep duration.
Lead author Odessa S. Hamilton from UCL Institute of Epidemiology & Health Care stated, “We have this chicken or egg scenario between suboptimal sleep duration and depression, they frequently cooccur, but which comes first is largely unresolved. Using genetic susceptibility to disease, we determined that sleep likely precedes depressive symptoms, rather than the inverse.”
For the study, data was collected from 7,146 individuals enrolled in the English Longitudinal Study of Ageing (ELSA), a nationally representative population study in England. The researchers used genetic and health data to determine the genetic predisposition to short sleep and depression in the participants.
Senior author Dr. Olesya Ajnakina from UCL Institute of Epidemiology & Health Care and the Institute of Psychiatry, Psychology & Neuroscience at King’s College London commented, “Short and long sleep durations, along with depression, are major contributors to public health burden that are highly heritable. Polygenic scores, indices of an individual’s genetic propensity for a trait, are thought to be key in beginning to understand the nature of sleep duration and depressive symptoms.”
In addition to the genetic findings, the researchers also examined non-genetic associations between depressive symptoms and sleep duration. Individuals who slept five hours or less were 2.5 times more likely to develop depressive symptoms, while those with depressive symptoms had a one-third increased likelihood of experiencing short sleep. The results were adjusted to account for various factors such as education, wealth, smoking status, physical activity, and longstanding illness.
Interestingly, the researchers also found a connection between sleeping longer and developing depressive symptoms. Participants who slept longer than nine hours were 1.5 times more likely to experience depressive symptoms compared to those who slept an average of seven hours. However, unlike the genetic findings, depressive symptoms were not associated with longer sleep duration four to 12 years later.
Professor Andrew Steptoe, Head of Behavioral Science and Health at UCL Institute of Epidemiology & Health Care, emphasized the importance of understanding the link between depression and lack of sleep, especially as both conditions increase with age due to worldwide population aging. He stated, “This study lays important groundwork for future investigations on the intersection of genetics, sleep, and depressive symptoms.”
In summary, the study provides valuable insights into the relationship between sleep duration and depressive symptoms. It suggests that consistently sleeping less than five hours per night may heighten the risk of developing depression. The findings also highlight the hereditary component of both sleep duration and depression, laying the foundation for further research in this field.