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People who fail to follow their natural body clock rhythm are more likely to have depression and mental health problems, a study has found.
Those who are inactive during the day and more active or restless at night have an increased risk of depression, bipolar disorder and low mood.
The findings come from the largest study of its kind, involving more than 91,000 people across the UK.
It was carried out by University of Glasgow researchers, who say disruption to normal circadian rhythms, which work on a 24-hour sleep/wake cycle, is associated with a greater susceptibility to mood disorders.
Those who took part had their activity levels monitored over a week.
Professor Daniel Smith, professor of psychiatry at the university, said: ‘A healthy rhythm is to be quite active during the day and very inactive at night.
‘This is an important study demonstrating a robust association between disrupted circadian rhythm and mood disorders.’
The study found those who did not follow the natural cycle were more likely to have mood disorders such as severe depression and bipolar disorder.
They were also more likely to feel lonely and less happy.
Professor Smith added: ‘There are a lot of things people can do, especially during the winter, such as getting out of the house in the morning to get exposed to light and take exercise, so that by evening they are tired.
‘You can also turn off your mobile phone around 10pm because the light in it is telling your brain it’s daytime. But it is hard for some people, such as shift workers, because of their job or because of their family circumstances.’
It is already known that the internal body clock regulates many functions including body temperature and eating habits.
Long-term night-shift work has previously been associated with an increased risk of cancer, heart disease and obesity.
However, the researchers say it is still not certain whether an out-of-kilter body clock causes mental health problems, or if the mental health problems are causing disturbances to people’s daytime and night-time cycles. They plan to investigate this next.
The researchers analysed activity data in 91,105 participants aged 37-73 from the UK Biobank, a large study group taken from the general population.
The researchers found that those who did not follow the natural rhythm had a greater likelihood of major depression or bipolar disorder and were also more likely to suffer worse wellbeing such as lower happiness levels.
Writing in journal The Lancet Psychiatry, Dr Aiden Doherty, senior research fellow from the University of Oxford’s Nuffield Department of Population Health, said a next step could be to carry out further research on younger people.
He added: ‘The circadian system undergoes developmental changes during adolescence, which is also a common time for the onset of mood disorders.
‘It might be that the UK Biobank provides the impetus for a resource of a similar scale in adolescents and younger adults to help transform our understanding of the causes and consequences, prevention and treatment of mental health disorders.’