Obsessive-compulsive disorder (OCD) is more common in people living in areas of high latitude, likely because of the effect of decreased sunlight on circadian rhythms, new research suggests.
Investigators reviewed studies from more than 200 countries and identified 24 estimations of lifetime prevalence of OCD in the general population.
They found that the prevalence of OCD increased as latitude increased, even when controlling for other potential factors. The prevalence of panic disorder, which was used as a "psychiatric control," was not significantly related to latitude.
Areas of high latitude receive less sunlight. This may exacerbate the tendency of individuals with OCD to experience sleep disturbances, owing to a "misalignment" between the sleep-wake cycle and the natural light-dark cycle.
"Our results, in combination with others, suggest that having a delayed sleep schedule may be associated with OCD," lead author Meredith Coles, PhD, professor of psychology, Binghamton University, New York, told Medscape Medical News.
"This is a good reminder to make sure that all our patients' basic needs are met — for example, that they have adequate food, water, a safe place to live, and are getting adequate sleep," she said.
The study was published online June 15 the Journal of Obsessive-Compulsive and Related Disorders.
"Based on past clinical observations and subsequent research, we have established a link between obsessive-compulsive symptoms and the timing of sleep," Coles said.
"Maintaining synchrony between sleep timing and the natural light-dark cycle is important for cognitive and emotional functions," she said.
"Individuals who have difficulty going to sleep until very late and waking up late are often not exposed to sunlight until later in the day and may therefore experience misalignment," she explained.
"We have known for about 10 years that people with OCD who seek intensive levels of treatment are also showing disruptions in the timing of their sleep at much higher rate than in the general population, but have not yet understood what, if anything, this connection means," study coauthor Jacob Nota, PhD, formerly of Binghamton University and currently a postdoctoral fellow at Harvard Medical School/McLean Hospital, Boston, Massachusetts, told Medscape Medical News.
"One possibility that we have been investigating is whether individuals with OCD are more likely to have disruptions in their circadian rhythms," he recounted.
The current study was one way "to test the hypothesis about the connection between OCD, biological circadian rhythms, and sleep, and since the data about how many people have OCD in populations all over the world exist, it seemed we could look at the relation with where the data were collected as a unique way to test if we are on to something," he added.
To test the hypothesis, the researchers conducted a literature search of publications through 2017, spanning 233 countries.
To be included, a study was required to include OCD prevalence, as assessed by an interview (eg, the SCID) and conforming to DSM-III, DSM-IV, or ICD-10 diagnostic criteria for OCD.
OCD estimates were matched and paired to an estimate for panic disorder. Panic disorders taken either from the study/dataset or were matched to a similar estimate for panic, based on the region sampled, the year the data were published, and the version of diagnostic criteria that were used.
Latitude was recorded for each nation as the absolute value of degrees from the equator.
If no information regarding specific locations within the country was available, the latitude of the capital city was used.
Of the initial 117 studies reviewed, 36 met inclusion criteria, yielding 60 estimates of the prevalence of COD. Of those, 24 were lifetime prevalence rates.
Many estimates came from Asia (n = 6) and North America (n = 10); fewer came from other countries (n = 9).
Using Pearson correlation coefficient, the researchers found that lifetime prevalence of OCD was significantly associated with latitude (r = .64, P < .001).
The prevalence of OCD was higher in regions further from the equator.
Moreover, both the maximum and minimum numbers of daily hours of sunlight were related to prevalence; longer periods of sunlight were associated with lower rates of OCD, and shorter periods of sunlight were associated with higher rates of OCD.
These findings remained, even after controlling for individual factors (eg, sex and marital status), community factors (eg, gross domestic product), and study-specific factors (eg, sample size, year).
The impact of latitude seemed unique to OCD rather than to broader mental health problems — a parallel analysis found no relationship between panic disorder and either latitude or amount of sunlight per day.
"On some level, this [study finding] is what we thought we might find, but what was surprising is the strength of the relation between OCD prevalence and latitude, [which is] a fairly strong correlation [and] means that more people with OCD are found at places further from the equator," Nota commented.
"It was also very interesting that we did not find a meaningful relation between the prevalence of another type of anxiety — panic disorder — and latitude, which means that it's not that you find more anxiety disorders or more disorders in general at higher latitudes," he continued.
"Further, this relationship couldn't be explained away by some likely alternatives, such as how many people were included in the study we looked at, the year each study happened, characteristics of the people included, or the wealth of nations being examined," he said.
He suggested that there is "a possibility that OCD is uniquely 'tangled' with the timing of sleep and that people with OCD may more frequently drift toward delayed sleep in relation to their environment."
Being in that condition "may then contribute to difficulties disengaging from intrusive obsessive thoughts or resisting the urge to engage in compulsions," he explained.
Commenting on the study for Medscape Medical News, Nicole Short, MS, a doctoral candidate at Florida State University, Tallahassee, who was not involved with the research, said the study extends previous research indicating that OCD is "uniquely associated with disruptions in our circadian rhythms — specifically, that those who tend to have an evening preference ('night owls') are at greater risk for OCD."
Testing whether this association applies not only to individual differences but also to "outside factors, like where we live, is an interesting and novel idea," and the finding that OCD prevalence increases with latitude is "a new perspective that certainly deserves further investigation," she said.
"The study emphasizes the fact that clinicians treating OCD really need to ask patients about their sleep, and not just insomnia but also the timing of sleep — particularly if they are finding traditional OCD treatments are not as effective as they'd expect — and consider whether intervening on sleep would be an appropriate avenue," said Short.
Nota added that addressing delays in the timing of sleep and intervening with biological circadian rhythms will help people with OCD to "stay in time with the environment" and may also help them to "engage in treatment for OCD and/or help symptoms directly."
The study received no external funding. Dr Coles, Dr Nota, the other coauthors, and Nicole Short have disclosed no relevant financial relationships.
J Obsessive Compuls Relat Disord. Published online July 15, 2018. Abstract
Medscape Medical News © 2018
Cite this: Areas of Higher Latitude Tied to Elevated OCD Risk - Medscape - Jul 23, 2018.