What is circadian depression? It may help explain your sleep problems

Depression can present in similar ways, but the causes behind it can differ.

Symptoms such as fatigue, low mood and low energy may appear alike from person to person, yet depression is a complex condition that can stem from multiple factors and include several subtypes.

New research has pointed to a subtype that may be linked to the body’s internal clock, disrupting sleep and leaving people feeling as though they are permanently jet-lagged.

Because depression has many possible causes, researchers have been examining biological factors that could be behind the symptoms, including the circadian rhythm, or body clock.

The circadian clock is the body’s 24-hour cycle, which helps regulate hormones, digestion, mood and the sleep-wake pattern.

“When it’s off, you feel jet-lagged all the time,” lead researcher Ian Hickie told ScienceAlert. “You feel tired, you feel exhausted, you gain weight, you can’t concentrate, you sleep poorly and your behavior changes.”

The study, published in the British Journal of Psychiatry, found that one in four people with depression may have “circadian depression” driven by an out-of-sync body clock.

Using data from 11,380 participants in the Australian Genetics of Depression Study, the researchers found that a quarter of them met at least three of six criteria used to define the circadian depression subtype.

One criterion is that symptoms vary with the seasons as daylight hours shorten.

Another is that the midpoint of sleep — the halfway point between falling asleep and waking up — is delayed compared with the general adult population, usually falling between 2 and 4 a.m.

People with circadian depression also experience social jet lag, meaning their sleep midpoint differs by several hours on workdays versus non-working days. Their sleep schedule therefore does not match the timing around which most of society is organized.

Another sign is an evening chronotype, which earlier research has suggested may contribute to more depressive symptoms because staying up later can increase poor decisions and impulsive behavior.

The final two criteria were sleeping longer than average when given the opportunity and reporting strong morning tiredness.

The study also found that participants with circadian depression experienced more side effects from antidepressants and were less likely to benefit from the treatment.

“Depression is not a uniform illness and understanding the characteristics of different subtypes mean that we can give people earlier access to treatments that will be most effective for them,” first study author Emiliana Tonini told ScienceAlert.

According to the study, people in the circadian subtype were more likely to gain weight during depressive episodes, faced a higher risk of inflammatory and cardiovascular problems, and were more likely to have neurodevelopmental disorders such as ADHD.

They also tended to experience depression earlier and reported more severe symptoms, including mania, psychosis and suicidality.

Because standard medications appear to work less well for this subtype, and because it is tied to the body’s internal clock, the researchers suggest focusing treatment on circadian rhythm itself, including light therapy and melatonin.