Both sleep duration and depression are partly inherited from one generation to the next, according to researchers.
The study led by UCL (University College London) researchers and published in the journal Translational Psychiatry, analysed data from people with an average age of 65 and found short sleep was associated with the onset of depressive symptoms.
“Using genetic susceptibility to disease we determined that sleep likely precedes depressive symptoms, rather than the inverse,” said lead author Odessa S. Hamilton.
For the study, the researchers used genetic and health data from 7,146 people recruited by the English Longitudinal Study of Ageing (ELSA), a nationally representative population study in England.
They found that people with a stronger genetic predisposition to short sleep (less than five hours in a given night) were more likely to develop depressive symptoms over 4-12 years, but that people with a greater genetic predisposition to depression did not have an increased likelihood of short sleep.
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,” said senior author Dr Olesya Ajnakina.
The research team also looked at non-genetic associations between depressive symptoms and sleep duration.
They found that people sleeping five hours or less were 2.5 times more likely to develop depressive symptoms, while people with depressive symptoms were a third more likely to suffer from short sleep.
They adjusted for a rich selection of factors that could affect the results such as education, wealth, smoking status, physical activity and limiting longstanding illness.
The researchers also found a link between sleeping long and developing depressive symptoms, with participants sleeping longer than nine hours being 1.5 times more likely to develop depressive symptoms than those who sleep an average of seven hours.
However, depressive symptoms were not associated with sleeping longer four to 12 years later, which corresponded to the genetic findings.
“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,” said professor Andrew Steptoe.