Scientists identify a new type of depression affecting 1 in 4 patients

Researchers from the University of Sydney have identified a new subtype of depression in a recent breakthrough.

Named “circadian depression”, it is directly linked to disruptions in the body’s 24-hour internal clock which is the sleep-wake cycle.

A large study published in the British Journal of Psychiatry found that 1 in 4, which is 26 percent, people with severe depression met the criteria for this type of depression where body clock disruptions contribute to their mental illness.

"Depression is not a uniform illness and understanding the characteristics of different subtypes means that we can give people earlier access to treatments that will be most effective for them," said Emiliana Tonini, an author of a new study detailing the condition published in the British Journal of Psychiatry.

Speaking about the symptoms of circadian depression, the patients experience more severe symptoms that begin at a younger age compared to other forms of depression. Among all genders, it affects females.

People who suffer from this subtype are less likely to respond to conventional antidepressants.

It is characterized by disrupted sleep, excessive daytime sleepiness, low energy and reduced daytime physical activity.

Such people are also vulnerable to higher genetic risk factors for ADHD, anxiety and major depressive disorders. They are also linked to increased risk of inflammation and disrupted metabolism.

"For those who find that antidepressants are not working for them, it is important to speak to your clinician for advice about your individual circumstances."

Proposed diagnostic criteria

To be classified as having circadian depression, individuals must meet at least three of the following six criteria:

• Excessive daytime sleepiness
• Feeling tired in the morning
• Preference for staying up late
• Seasonality based on mood changes influenced by light and day length
• Delayed sleep patterns
• Social jet lag: a mismatch between biological clocks and social schedules

Such patients respond better to treatments targeting body-clock brain circuits, such as: Light therapy, Melatonin and Melatonin-targeted antidepressants.

Clinicians are advised to consider circadian-targeted treatments much earlier for patients presenting with these specific symptoms.