If you happen to be staying up tonight, you may want to think twice before burning the midnight oil. A newly published study, which examined more than 91,000 people, linked a disrupted internal clock (being active at night or inactive during the day) with the development of mood disorders.

The paper titled "Association of disrupted circadian rhythmicity with mood disorders, subjective well-being, and cognitive function" was published in the journal The Lancet Psychiatry on May 15.

Researchers from the University of Glasgow in the U.K. noted that a regular sleep-wake cycle is "crucial" for mental health and well-being, as they associate certain forms of disruption with mood disorders such as depression and bipolar disorder.

"Although several studies have identified associations between disrupted circadian rhythmicity and adverse mental health outcomes, much of this work has limitations," they wrote. Limitations of previous research included inaccuracies due to self-reporting, small sample size, or lack of adjustments for potential confounders. 

For the large study, the researchers examined activity data of 91,105 people from the U.K. who were aged between 37 to 73 years. The participants wore activity monitors for a week which measured how disrupted their body clocks were.

The findings revealed that those who were active during the night or inactive during the day were 6% to 10% more likely to be diagnosed with a mood disorder. This was in comparison to participants who followed a normal cycle of being active during the day and switching to rest at night.

But Dr. Laura Lyall, study author and research associate at the University of Glasgow, highlights a chicken-and-egg problem since the study was an observational one. In other words, the findings cannot determine whether it was the disrupted internal clock which caused the mood disorder or vice versa. 

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.

"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 well-being and cognitive ability," Lyall said.

Indeed, numerous researchers have expressed concern over the adverse health effects caused by working night shifts or excessively using electronics around bedtime.

A study from 2016 found that using bright screen devices (the most popular culprit being smartphones) in bed could strain and damage the eyes over time. Another study published in April this year suggested that people who often stay up at night were more likely to experience diabetes, psychological disorders, neurological disorders, and early death.

Lyall added that a longitudinal study in younger populations in which they "track participants' rest-activity patterns over time" could help establish cause and also design treatments to predict and reduce the risk of developing mood disorders.