Australian researchers have identified a new subtype of depression – termed “circadian depression” – linked to disruptions in the body’s internal clock, which they believe is less responsive to traditional antidepressant treatments. In a study published in British Journal of Psychiatry, involving clinical and genetic data from 11,380 Australians with mostly severe and recurrent depression, researchers identified circadian depression as affecting nearly a quarter (23%) of participants. They suggest people affected by the subtype may benefit from treatments that target the body’s circadian rhythms, such as melatonin and light therapy.
While a link between mood disorders and disrupted daily rhythms has been known for some time, the researchers say the “study strengthens the evidence base for a circadian subtype of depression as a biologically valid and clinically useful phenotype of depression”. The study’s first author, Dr Emiliana Tonini of the University of Sydney’s Brain and Mind Centre, said the researchers defined circadian depression as being in participants who showed at least three out of six features: experiencing a seasonal pattern of illness, delayed sleep timing, sleeping longer when depressed, being a night owl, waking feeling very tired, and social jetlag – when “their sleep when they go to bed during the week or when they work is very different from the weekend or when they are free to organise their day”. Prof Ian Hickie, a psychiatrist and co-director of the Brain and Mind Centre, said: “What is critical about being in this circadian type is its poor response to the standard therapies, those which are typically recommended in the guidelines.” SSRIs and SNRIs, typical first-line antidepressant drugs, were less effective and had more side effects for people with the circadian subtype, the study found.
For those with circadian depression, “chronobiological treatments – things focused on the sleep-wake cycle, particularly … to do with morning light exposure, daylight activity, regularity of sleep-wake cycles, regularity of food schedules, is critical”, Hickie said. In their study, the researchers noted that the participants were “were limited to those of genetically inferred European ancestry, which may limit generalisability”, and that “future studies are needed to replicate our findings in diverse samples”. The director of the Monash Alfred Psychiatry Research Centre, Prof Jayashri Kulkarni, who was not involved in the research, described it as a “really well-conducted study”.
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