Prof Smith said this study is important on a global scale 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".
"To look at this in more detail, it will be useful for future studies to track participants' rest-activity patterns over time to see whether disturbed rhythms can predict whether someone is more likely to go on to develop a mood disorder", commented author Dr Laura Lyall from the University of Glasgow.
The results held true even when the potential impact of factors such as old age, unhealthy lifestyle, obesity, and childhood trauma were taken into account, they reported in The Lancet Psychiatry, a medical journal.
Researchers of this study analyzed activity data from 91,105 participants (aged, 37-73 years) from the UK Biobank general population cohort to obtain the relative amplitude of the study population (a variable to determine the degree to which circadian rhythms of rest-activity cycles is disrupted). "I don't think it's unreasonable to say this is another piece of evidence that might suggest we should all be more mindful of our natural rhythms of activity and rest", Professor Smith explained.
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.
All participants wore accelerometers for seven days between 2013 and 2015 to record their activity. This information was linked to mental health questionnaires to assess symptoms of mental disorders and subjective wellbeing and cognitive function. Circadian disruption was also associated with lower well-being, higher neuroticism, increased loneliness, less happiness and health satisfaction, more mood swings, and a slower reaction time.
The scientists found that people who experienced more circadian disruption were between 6% and 10% more likely to have been diagnosed with a mood disorder than people who had more typical sleep cycles.
But the findings "reinforce the idea that mood disorders are associated with disturbed circadian rhythms", said Lyall.
"The circadian system undergoes developmental changes during adolescence, which is also a common time for the onset of mood disorders", he added. "It might be that the UK Biobank provides the template and 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".
 Quotes direct from authors and can not be found in text of Article. The researchers objectively measured the rest and activity rhythm patterns which is known as relative amplitude.
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