Sleeping less than five hours a night could raise the risk of developing symptoms of depression, research suggests.
The link between poor sleep and mental ill health is well known, but it has been unclear which problem tends to come first. Now scientists have found evidence that consistent short sleep at night can be a precursor to developing depressive symptoms.
“We have this chicken or egg scenario between suboptimal sleep duration and depression. They frequently co-occur, but which comes first is largely unresolved. Using genetic susceptibility to disease we determined that sleep likely precedes depressive symptoms, rather than the inverse,” said Odessa Hamilton, a PhD candidate at UCL and first author of the research.
The researchers looked at genetic and health data from 7,146 people recruited by the English Longitudinal Study of Ageing (ELSA). Both sleep duration and depression are partly inherited. Earlier research shows that depression is about 35% heritable, and that genetic differences account for 40% of the variance in sleep duration.
When the study’s subjects were tracked over time, researchers found that people who were genetically predisposed to short sleep (less than five hours a night) were more likely to develop depressive symptoms over four to 12 years, but that people more genetically predisposed to depression were not more likely to suffer from problems sleeping.
Overall, the participants in the study had an average of seven hours’ sleep a night. More than 10% slept for less than five hours a night at the start of the study period, rising to more than 15% at the end of the study period, and the proportion of participants classed as having depressive symptoms increased from around 9% to 11%.
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.
The findings might present a gloomy outlook for those already struggling with sleep disturbances. However, Hamilton said that poor sleep or depression should not be viewed as inevitable outcomes and that the findings underlined the importance of sleep for good mental health.
“My advice would be to prioritise sleep and to avoid sleep procrastination. There’s this common saying in genetics that genes load the gun and environment pulls the trigger. You might be genetically predisposed to this, but you can take steps to mitigate the risk.”
The findings are published in the journal Nature Translational Psychiatry.
