If the participants was highly active at late hours, or inactive during the day, this was classed as a disruption, Business Insider reports. The internal clock figures out the current time of the day by using the cues from sunlight and then transmits the information to the peripheral clocks located in the entire body.
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.
"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.
Daily circadian rhythms govern fundamental physiological and behavioural functions from body temperature to eating habits in nearly all organisms. With the data, circadian relative amplitude, which is a measure of the extent to which circadian rhythmicity of rest-activity cycles is disrupted, was evaluated.
"It's a cross-sectional study, so we can't say anything about cause and effect or what came first, the mood disorder or the circadian disruption", said Kristen Knutson, associate professor of neurology at Northwestern's Feinberg School of Medicine, who was not involved in the study.
In addition to increased risk of depression and bipolar disorder, lower relative amplitude was also associated with low subjective ratings of happiness and health satisfaction, with higher risk of reporting loneliness, and with slower reaction time (an indirect measure of cognitive ability).
The results of the study revealed that the people who had a disrupted body clock were more likely to get the symptoms for major bipolar disorder and depression.
Additionally, the study population was "not ideal" according to Dr. Aiden Doherty from the University of Oxford in England, who added that 75% of mental health disorders start before the age of 24 years.
This study was funded by the Lister Institute of Preventive Medicine. "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".
Researchers in the United Kingdom made the conclusion by studying the circadian rhythm: our waking and sleeping patterns throughout the 24-hour sleep cycle.