What is ‘circadian depression’?

The link between depression and disrupted daily rhythms has long been recognised. But research has now suggested there is a whole new subtype of depression – “circadian depression” – caused by “people’s body clocks being out of whack”, said New Scientist.

It affects an estimated one in four people with severe depression, according to a large-scale population and genetics study published in the British Journal of Psychiatry. But treatment with standard antidepressants like SSRIs seems to be less effective, and causes more side effects.

What is ‘circadian depression’?

It is “characterised by disrupted sleep, low energy and reduced physical activity during the day”, said Nature. It appears to be linked to dysregulation in the body’s internal clock and seems to affect women more than men. Depressive symptoms tend to start at an earlier age than with other forms of depression, and, although seasonality can aggravate them, it doesn’t necessarily trigger them, like seasonal affective disorder does.

The study researchers asked 11,380 people with severe depression to fill out surveys about changes in their symptoms and sleep patterns. Nearly a quarter (23%) met at least three of the researchers’ six proposed criteria for circadian depression. This was “not a formal diagnosis”, said The New York Times, but evidence of a “suggested subtype”. The criteria are: waking up feeling “very tired” regardless of sleep duration; identifying as a “night owl”; going to sleep later than most people; sleeping longer when most depressed; sleeping in on non-working days, and experiencing strong seasonal changes in sleep, mood, appetite or energy.

Moreover, analysis of participants’ saliva indicated that those who fell into the proposed subtype had genetic variants linked to a higher risk of developing ADHD, bipolar disorder, anxiety, a high body-mass index and insulin resistance. This indicates that circadian depression is “not just depression with bad sleep, but actually there is an underlying biology that is quite distinct from other forms of depression”, the study’s lead author, Emiliana Tonini of the University of Sydney’s Brain and Mind Centre, told the press.

How might it be treated?

What’s “critical” about this circadian type of depression is “its poor response to the standard therapies”, study co-author Ian Hickie, a psychiatrist at the Brain and Mind Centre told The Guardian. Those affected could benefit instead from treatments, such as melatonin or light therapy, that specifically target the body’s circadian rhythms .

The coordination of your body clock “underpins your mood, your metabolism, your concentration, your sleep-wake cycle and many other key factors”, said Hickie. You can help reset your body clock by exposing yourself to daylight in the morning and maintaining the rhythm and regularity of your sleep-wake cycle, while avoiding artificial light, large meals and exercise once it gets dark.

“Light is the most powerful signal for keeping our circadian rhythms in sync with the outside world,” Sophie Bostock, founder of The Sleep Scientist, told The Independent. “It helps us feel alert during the day and supports the timing of sleep at night.” In the autumn, after the clocks go back and mornings are dark, try to find an opportunity to get outside during working hours. “Even on a cloudy winter day, outdoor light is usually much brighter than indoor lighting.”

What are the caveats to the study?

Circadian depression is “a plausible” condition, said US chronotherapeutics expert Michael Terman. But the study findings don’t establish a new diagnosis, or prove that circadian depression will respond to different types of treatment, he told The New York Times.

A “significant limitation” of the study, acknowledged by its authors, was that the participants “self-reported their sleep-wake cycles”. It’s not clear whether “they did so accurately”. They were also mostly of European ancestry, which “may limit generalisability”. Further, more diverse studies are “needed to replicate our findings”, the researchers said.

The study also didn’t consider the impact of menopause, which is “predominantly one of the things that women describe as causing sleep disturbance”, Australian psychiatry professor Jayashri Kulkarn told The Guardian. But managing to tie “certain types of depression to a specific genetic profile” will be “important for onward treatment”.