New study suggests people with OCD are especially sensitive to the seasons

The clocks have gone back and there's a chill in the air. It's well known that during these darker months, a significant minority of us experience unwelcome negative changes to our mood (at least if you believe in the notion of Seasonal Affective Disorder or SAD, which not all experts do). Now an intriguing study in Psychiatry Research has explored the link this condition may have with another psychiatric diagnosis, Obsessive Compulsive Disorder (OCD).

The results suggest that people with OCD are more likely than average to experience seasonal effects on their mood, and that for these seasonally sensitive people with OCD, their "compulsions" are worse in the colder months.

It's already established that some of the underlying neurophysiology of SAD and OCD is the same, involving dysfunction of the neurotransmitter serotonin, note the study authors Oğuz Tan and his colleagues at Uskudar University in Turkey. They also point to past research that has shown the prevalence of OCD is highest in Autumn, and that light therapy, used to treat SAD, has been shown to benefit some people with OCD.

To further study the links between OCD and SAD, Tan and his team recruited 104 people in Istanbul diagnosed with OCD (and most of whom were on drug treatments) and 125 local controls without OCD (controls were included if they had other mental health problems, unless they were considered too severe, such as a diagnosis of schizophrenia or bipolar disorder). All participants completed a comprehensive questionnaire about their sensitivity to seasonal effects on mood and behaviour, including sleep and social activity. The participants diagnosed with OCD also completed a questionnaire about their OCD-related symptoms.

The participants with OCD reported greater seasonal sensitivity (mostly to colder months) – in fact, based on the extremity of their scores and how much they felt the effects were problematic, 19 per cent showed signs of SAD compared with just 9 per cent of the controls. What's more, among this sub-group who had OCD combined with SAD, their depression symptoms and compulsions (the actions or thoughts they perform to cope with their disturbing thoughts or mental images) were worse when they were tested in their least favoured time of year. Finally, when participants with OCD and Winter/Autumn-related SAD were tested in these cooler months, the severity of their compulsions correlated with the shortness of the daylight hours on the day of testing.

"Our results indicate that seasonal changes in mood frequently co-occur with OCD, which denotes that OCD and mood seasonality may share a common etiology," the researchers said.

They don't know why there was a seasonal association with OCD-related compulsions but not "obsessions" (troubling thoughts or mental images). They also acknowledged their study's drawbacks, including the dependence on participants' own reports of their OCD and SAD-related symptoms (the measure of seasonal sensitivity in particular is not a true diagnostic test), and the cross-sectional design. More convincing would be to measure people's OCD-related symptoms over time and see if they fluctuate with the seasons.

Tan and his colleagues believe the topic merits further study, especially to determine "the effect of SAD on the quality of life, prognosis, and risk of suicide and treatment response in patients with OCD".