New Depression Research: Body Clock Disruption May Be the Root Cause
For decades, the medical community assumed that circadian disruption in depression was merely a side effect — fix the depression, and the sleep problems would resolve. But new research challenges that notion: for about 30% of people with depression, it's the other way around — a disturbed body clock is actually driving the depression.
"If it's not attended to, you won't fix the episode of depression, and you won't prevent its longer-term recurrence," says Professor Ian Hickie of the University of Sydney's Brain and Mind Centre. This finding could change the way many people with depression are treated.
Could Common Antidepressants Make Things Worse?
The research raises an alarming possibility: the most commonly recommended treatments — cognitive behavioral therapy (CBT) and particularly SSRIs — may not only fail to work for this "circadian subtype" but could actually make it worse.
The reason relates to light, the most important factor in setting our body clock each day. Healthy light patterns — bright light during the day and low or no light at night — are associated with a lower risk of depression. SSRIs increase circadian sensitivity to light: useful if you get light at the right time, but for night owls exposed to bright light late at night, this enhanced sensitivity can exacerbate circadian disruption and potentially worsen depressive symptoms.
Professor Sean Cain of Flinders University explains a striking pattern: "People are three times more likely to use darkness metaphors if they have severe depression. We think that the circadian system is a brightness detection system, and that people experience depression as a feeling of darkness because this brightness detection system isn't working."
Who Is Affected by the Circadian Subtype?
According to the new study, the following groups are most commonly affected:
- Women: 80% of those affected were female, though more women participated in the study. Hormonal and environmental changes such as childbirth play a role — the circadian subtype is particularly relevant to postnatal depression.
- Those with severe symptoms: More common in people with severe depression.
- Those with adolescent or early-adult onset: The sleep-wake cycle changes radically during adolescence, a key environmental trigger.
"Some of us are much more sensitive and essentially have much more unstable clocks — it's the extent to which it can be perturbed and does not self-correct," Hickie explains. "The biology's fundamentally different, underpinned by differential genetics, but then dependent on environmental exposures" such as adolescence, a new baby, shift work, an infection, or regularly staying up late.
Practical Tips for Better Sleep and Mood
While research into targeted treatments (such as melatonin and melatonin-targeted antidepressants) continues, experts offer practical advice you can act on now:
- Set a consistent wake-up time: Wake within the same one-hour window every day, even on weekends. "It's much easier if you set the wake-up time," says Hickie. "People tend to do the opposite — they'll go to bed at 10 o'clock and then they can't go to sleep."
- Track your sleep and light exposure: Write it down over several days and bring it to your clinician. Some smartwatches, such as the Apple Watch, detect time in daylight and sleep regularity.
- Get natural daytime light: Seek bright natural light during the day and dim the lights at night.
- Stay physically active: Daytime physical activity has a much bigger impact on sleep than worrying about it at 10 pm.
- Stop eating after dark: Eating after melatonin onset may interfere with insulin regulation.
"If you want to sleep better tonight, the amount of light exposure you have today and the physical activity will have much bigger impact than starting to worry about it at 10 o'clock at night," Hickie says.
Professor Michael Berk, chair of psychiatry at Deakin University, calls the study "a very important start" in defining a new subtype, though further research is needed before it can definitively inform clinical practice.
For those looking to monitor their sleep and mood health, the Xiaoshu Health App can sync with Apple Health to track relevant metrics, helping you record sleep regularity and daylight exposure to share with your doctor.