What Is the Circadian Rhythm? Disrupted Body Clock Linked to Depression in New Study

A disrupted body clock has been linked to an increased risk of developing mental disorders, including depression and bipolarity, in a new study.

Researchers in the U.K. made the conclusion by studying the circadian rhythm: our waking and sleeping patterns throughout the 24-hour sleep cycle.

Laura Lyall, research associate in mental health and wellbeing at Glasgow University and lead author of the study, said in a statement: "In the largest such study ever conducted, we found a robust association between disruption of circadian rhythms and mood disorders.

"Previous studies have identified associations between disrupted circadian rhythms and poor mental health, but these were on relatively small samples."

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. The individuals wore an activity-tracker on their wrist for a week between 2013 and 2015.

The researchers used the resulting information to calculate what is known as the relative amplitude.

This was done by noting how active individuals were in the busiest 10 hours of each day, which was compared to their least active five hours. 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.

Those with a lower amplitude were found to be at higher risk of mental issues, even when factors such as age, sex, smoking status, educational attainment and childhood trauma were taken into account.

According to the study published in The Lancet they were 6 percent more likely to develop depression, and 11 percent more likely to have bipolar disorder. Such individuals were also more likely to feel unhappy, lonely and unsatisfied with their health, and have slower reaction times.

Around one in 25 participants were about as active during the day as they were at night. These were "people who have very poor sleep hygiene, people on their mobile phones at midnight checking Facebook or getting up to make a cup of tea in the middle of the night," Daniel Smith, professor of psychiatry and senior author of the study, told the Times.

He added it is advisable to avoid activities that disturb the circadian rhythm after 10 p.m., but that activities during the day were just as important, giving the example of being outside in the morning during the winter months.

"People who are active during the day and sleep well at night, that is a very healthy profile.... They would have a high score in relative amplitude," he told The Guardian.

Further research is needed to pinpoint the potential genetic and environmental reasons why our circadian rhythm might be disrupted, and how this could affect a person's chances of developing depression and bipolar disorder, he said in a statement.