Could 'body clocks' play a role in depression? Study proposes a new 'circadian' subtype

Some people with depression sleep far more than average, wake up exhausted, habitually stay up late, and experience mood shifts with the seasons.

A new study suggests that these symptoms may cluster in a distinct subtype of depression that's tied to the body's internal clock.

While research has long linked a scrambled circadian rhythm to a risk of mood disorders, neuroscientists are now proposing that these disruptions define a specific form of depression that they call "circadian depression." First conceptualized in 2021 , the body-clock subtype may affect about 1 in 4 people with severe, recurrent or persistent depression, the researchers estimate.

In their new study, published Wednesday (Oct.

21) in The British Journal of Psychiatry , the team identified the subtype in about 2,600 people out of over 11,000 evaluated.

"Circadian depression is a biologically informed subtype," said study co-author Emiliana Tonini , a neuroscientist at the University of Sydney.

"Unlike subtypes defined mainly by symptoms, the core feature here is a disturbed circadian system, which common antidepressants may not fully address," Tonini told Live Science in an email.

The researchers think treatments that target the sleep-wake system, such as the sleep hormone melatonin or bright light therapy , might be beneficial for people with this subtype.

However, because the subtype is still a proposal and not formally established yet, other experts say that further research is needed before the findings can inform clinical practice.

More than just bad sleep Tonini and her team analyzed data from 11,380 adults ages 18 to 90 who took part in the Australian Genetics of Depression Study (AGDS) , a nationwide study exploring how genes and life experiences influence depression and responses to treatment.

They classified participants under the "circadian" umbrella if they had at least three of six features: seasonal mood swings, late sleep schedules, social jet lag (a mismatch between sleep routine during workdays and free days), night-owl habits , excessive sleep ( hypersomnia ), and fatigue upon waking.

A total of 2,604 people fit the proposed subtype.

Compared with others in the AGDS cohort, this group was younger and developed depression earlier in life — around 19, compared with about 23 for the rest of the cohort.

The group also skewed female, and individuals reported greater psychological distress, frequent suicidal thoughts and more physical complaints than people who didn't fit the proposed subtype.