In the study (.pdf), researchers used Google's public database of queries to identify and monitor users' searches for mental-health disorders, including anxiety, eating disorders, schizophrenia, ADHD, bipolar and obsessive compulsive disorder (OCD), in the United States and Australia from 2006 through 2010. According to a release:
The research showed eating disorder searches were down 37 percent in summers versus winters in the U.S., and 42 percent in summers in Australia. Schizophrenia searches decreased 37 percent during U.S. summers and by 36 percent in Australia.
Bipolar searches were down 16 percent during U.S. summers and 17 percent during Australian summers; ADHD searches decreased by 28 percent in the U.S. and 31 percent in Australia during summertime. OCD searches were down 18 percent and 15 percent, and bipolar searches decreased by 18 percent and 16 percent, in the U.S. and Australia respectively.
Searches for suicide declined 24 and 29 percent during U.S. and Australian summers and anxiety searches had the smallest seasonal change – down 7 percent during U.S. summers and 15 percent during Australian summers.
While some conditions, such as seasonal affective disorder, are known to be associated with seasonal weather patterns, the connections between seasons and a number of major disorders were surprising. "We didn't expect to find similar winter peaks and summer troughs for queries involving every specific mental illness or problem we studied, however, the results consistently showed seasonal effects across all conditions – even after adjusting for media trends," said James Niels Rosenquist, MD, PhD, a psychiatrist at Massachusetts General Hospital.
The work appears in the latest issue of American Journal of Preventive Medicine.