Disrupted Body Clock Linked to Mood Disorders

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The researchers found that a one-quintile reduction in relative amplitude correlated with increased risk of lifetime major depressive disorder and lifetime bipolar disorder (odds ratios, 1.06 and 1.11, respectively), as well as with greater mood instability (odds ratio, 1.02), higher neuroticism scores (incident rate ratio, 1.01), more subjective loneliness (odds ratio, 1.09), lower happiness (odds ratio, 0.91), lower health satisfaction (odds ratio, 0.90), and slower reaction times (linear regression coefficient, 1.75).

For the latest study, researchers analysed activity data on 91,105 people to measure their daily rest-activity rhythms (also known as relative amplitude).

Mathematical modelling was used to investigate associations between low relative amplitude (reflecting greater activity during rest periods and/or daytime inactivity) and lifetime risk of mood disorder as well as wellbeing and cognitive function.

To reach their findings, scientists at the University of Glasgow studied data collected on over 90,000 adults aged between 37 and 73 years old in the U.K, between 2006 and 2010.

Circadian rhythms are variations in physiology and behaviour that recur every 24-hours, such as the sleep-wake cycle and daily patterns of hormone release. People with less of a distinction between active and resting periods scored a lower amplitude, either because they were not active enough during while they were awake or too active in the hours intended for sleep. This was in comparison to participants who followed a normal cycle of being active during the day and switching to rest at night.

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The results held true even after adjusting for a wide range of influential factors including age, sex, lifestyle, education, body mass index, and childhood trauma.

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. Circadian rhythms occur in plants, animals and throughout biology.

Previous research has identified associations between circadian disruption and poor mental health, but these were typically based on self reports of activity and sleeping patterns, had small sample sizes, or adjusted for few potential confounders.

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". According to the study, one of the harmful effects of a disrupted body clock is a higher risk for mental health issues.

But the findings "reinforce the idea that mood disorders are associated with disturbed circadian rhythms", said Lyall.