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.
Data were included for 91,105 participants. This was in comparison to participants who followed a normal cycle of being active during the day and switching to rest at night.
For the large study, the researchers examined activity data of 91,105 people from the United Kingdom who were aged between 37 to 73 years.
While the study does not reveal whether disruptions to circadian rhythms are a cause of mental health problems, a result of them or some mixture of the two, the authors say the findings highlight the importance of how we balance rest and activity. Lower relative amplitude was also found to be reliably associated with greater mood instability, higher neuroticism scores, more subjective loneliness, lower happiness and health satisfaction, and slower reaction time (an indirect measure of cognitive function).
Dr Laura Lyall, lead author, said: "In the largest such study ever conducted, we found a robust association between disruption of circadian rhythms and mood disorders". A newly published study, which examined more than 91,000 people, linked a disrupted internal clock (being active at night or inactive during the day) with the development of mood disorders. This can be due to reduced activity during waking periods or increased activity during rest periods.
The scientists studied people's circadian rhythms, which control functions such as immune systems, sleep patterns, and the release of hormones, to measure the daily rest-activity rhythms, also known as the relative amplitude. A circadian relative amplitude variable was derived from these data, and the correlation with mood disorder, well-being, and cognitive variables was assessed. Disruption to these rhythms has been shown to profoundly affect human health. This meant those people who were up at their mobile phones at night or woke up for a snack or tea or a drink middle of the night.
According to Smith, these figures may appear small but are all significant. Smith added that it was striking that the link remained even when so many factors were taken into account.
DISRUPTION TO THE body's internal clock is associated with greater susceptibility to mood disorders such as severe depression and bipolar disorder, the largest study of its kind has found.
Based on the observational nature of the study, the researchers were unable to show causality, meaning it is unclear whether the sleep disturbances caused the mental health problems or vice versa. They recorded the activity of the individuals during the 10 active hours a day and compared it to the least active 5 hours a day.
"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", said Smith.