‘Circadian Depression’ May Overlap With Seasonal Depression, but Researchers Say It’s Not Identical

Seasonal affective disorder (SAD), a type of depression that waxes and wanes with annual weather patterns, seems to involve circadian rhythm disturbances, too, but it’s a much narrower concept, says Dr. Tonini.

Seasonal mood changes are only one of the six markers of circadian depression. In the study, about 41 percent of people with circadian depression had them.

People with circadian depression were also more likely to report a bipolar disorder diagnosis and to meet criteria for atypical depression, a type marked in part by sleeping too much and weight gain, says Kruse.

“Rather than completely separate kinds of depression, these features are likely distinct but overlapping dimensions of the illness,” she says.

Light Therapy May Help Depression, but Evidence for Melatonin Is Limited

The study didn’t test light therapy or melatonin, so it can’t show that these therapies especially benefit people with circadian depression, says Kruse.

“There is meaningful evidence that bright-light therapy can improve depression. Its role is best established in seasonal depression, but evidence also supports benefit in nonseasonal depressive disorders,” she says.

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“Melatonin is more complicated, and the evidence for improving depressive symptoms is much less established,” says Kruse.

Melatonin can help shift sleep earlier in people with a sleep disorder that pushes their sleep and wake times later, but whether it also eases depression in people with strong circadian features still needs to be tested, she says.

Research on whether melatonin improves mood in young people with circadian depression is currently underway, says Tonini.

Could Circadian Depression Become an Official Diagnosis?

Right now, circadian depression isn’t part of the Diagnostic and Statistical Manual of Mental Disorders (DSM), the standard guide U.S. mental health professionals use to classify mental disorders.

More research is needed before this could become an official diagnosis, says Tonini.

Kruse agrees, saying, “The findings are a signal for follow-up rather than the final definition of a new subtype of depression.”

Strengths and Limitations of the Study

The study was large and included genetic data, but it only captured a single point in time, so it can’t show that body clock problems cause depression, only that they’re linked.

Symptoms, sleep habits, and how well antidepressants worked were all self-reported, and the circadian markers came from questionnaires rather than direct measures of the body clock. All participants were also of European ancestry, so the findings may not apply to people of different races and ethnicities.

What to Ask Your Doctor if You Have Symptoms of ‘Circadian Depression’

If you feel like sleep may be a major factor in your depression, tracking your sleep and wake times for a few days with a wearable device or a sleep diary, and sharing that information with your provider, could help guide the conversation, says Tonini.

“I wouldn’t advise asking, ‘Do I have circadian depression?’” says Kruse.

Instead, she recommends describing the pattern you experience and asking targeted questions such as:

  • Could changing my sleep-wake schedule, or making it more consistent, help treat my depression or reduce the risk of future episodes?
  • If so, how should I approach this?
  • Does the seasonal pattern of my mood, energy, and sleep suggest that a treatment such as bright-light therapy might be worth considering?

It’s also important to share your full mood history with your doctor, says Kruse.

“Body clock problems are also common in bipolar disorder, so if your depression started at a young age or you’ve had periods of unusually high energy along with distinct mood changes, your doctor may need to look beyond depression and take a more cautious approach to treatment,” she says.