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.
Several mood disorders were tied to poor sleep and disruptions in circadian rhythms, researchers found. "However, these are observational associations and can not tell us whether mood disorders and reduced well-being cause disturbed rest-activity patterns, or whether disturbed circadian rhythmicity makes people vulnerable to mood disorders and poorer well-being".
Daily circadian rhythms govern fundamental physiological and behavioural functions from body temperature to eating habits in nearly all organisms.
Earlier research had suggested that disrupting these rhythms can adversely affect mental health, but was inconclusive: most data was self-reported, participant groups were small, and potentially data-skewing factors were not ruled out.
Regarding the research, he told: "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".
To assess these relationships, the researchers collected data on more than 91,100 individuals from the U.K. Biobank, between the ages of 37 and 73, excluding those who reported sleep apnea or insomnia.
All participants wore accelerometers for seven days between 2013 and 2015 to record their activity.
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. It was also associated with greater mood instability (OR, 1.02; 95% CI 1.01-1.04), higher neuroticism scores (incident rate ratio, 1.01; 95% CI 1.01-1.02), more subjective loneliness (OR, 1.09; 95% CI, 1.07-1.11), lower happiness (OR, 0.91; 95% CI, 0.90-0.93), lower health satisfaction (OR, 0.90; 95% CI, 0.89-0.91), and slower reaction times (linear regression coefficient, 1.75; 95% CI, 1.05-2.45).
"While our findings can't tell us about the direction of causality, they reinforce the idea that mood disorders are associated with disturbed circadian rhythms, and we provide evidence that altered rest-activity rhythms are also linked to worse subjective wellbeing and cognitive ability", said Dr Lyall. The participants' activity data was then linked to responses from their online mental health questionnaire.
Measurements of people's rest-work cycles could be a useful tool for flagging and treating people at risk of major depression or bipolar disorders, the researchers concluded.
People who fail to follow their natural body clock rhythm are more likely to have depression and mental health problems, a study has found. As the authors note, 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 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".
The study was funded by the Lister Institute of Preventive Medicine.