A study find that those of us more active at night are risking mental health problems, such as depression and bipolar disorder.
People who have their body clock disrupted by being awake at night risk developing mood disorders and depression.
That is the finding from a study of more than 90,000 people by scientists at the University of Glasgow.
The scientists examined people’s circadian rhythms, which control functions such as sleep patterns, immune systems and the release of hormones, to measure daily rest-activity rhythms, also known as relative amplitude.
People with lower relative amplitude were at greater risk of mental health problems such as depression and bipolar disorder.
They are also likely to feel less happy and more lonely, the study found.
Dr Laura Lyall, the study’s lead author, said the team had found a “robust association” between disruption of circadian rhythms and mood disorders.
“Previous studies have identified associations between disrupted circadian rhythms and poor mental health, but these were on relatively small samples.”
Daniel Smith, senior author of the paper, told The Times that using mobile phones late at night, waking in the early hours to make a cup of tea are among the things that affect sleep.
He said that a 10pm cut-off would give the average adult time to wind down before switching off the lights and going to sleep.
“But it’s not just what you do at night,” he said, “it’s what you do during the day – trying to be active during the day and inactive in darkness,” he said.
“Especially in the winter, making sure you get out in the morning in the fresh air is just as important in getting a good night’s sleep as not being on your mobile phone.”
Regarding the study, he said: “The next step will be to identify the mechanisms by which genetic and environmental causes of circadian disruption interact to increase an individual’s risk of depression and bipolar disorder.
“This is important globally because more and more people are living in urban environments that are known to increase risk of circadian disruption and, by extension, adverse mental health outcomes.”
The study is published in The Lancet Psychiatry.