The impact of latitude on the prevalence of seasonal depression.
BACKGROUND
This study sought to determine whether the prevalence of the seasonal subtype of major depression (SAD) in the community varied as a function of latitude.


METHODS
Random telephone numbers were generated across 8 degrees of latitude (41.5 degrees N to 49.5 degrees N) for the province of Ontario. Eight strata of 1 degree each were sampled equally throughout a 12-month period. Using a validated and structured diagnostic interview, we interviewed by telephone respondents over 20 years of age who had lived in the region for 3 years or more. We evaluated patterns of symptom change across seasons to establish a diagnosis of SAD according to DSM-IV criteria.


RESULTS
Of the 2078 households that were assessed for eligibility, 1605 (77%) completed the interview. The crude prevalence of lifetime SAD was 2.6% (95% CI, 1.9 to 3.5). There was no impact of latitude on prevalence of either major depression or the seasonal subtype across the 8 strata, although the global measure of the severity of seasonal change in mood was significantly negatively correlated with latitude.


CONCLUSIONS
SAD is a common subtype of major depression in Ontario, but there is no evidence to support an increase in prevalence with increasing latitude.
Levitt
Anthony J
AJ
Department of Psychiatry, Department of Nutritional Sciences, Fellowship Program, University of Toronto, Sunnybrook and Women's College Health Sciences Centre, Toronto, Ontario. anthony.levitt@swchsc.on.ca
Boyle
Michael H
MH
D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006306:Health Surveys; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009864:Ontario / Q000453:epidemiology; D012307:Risk Factors; D016574:Seasonal Affective Disorder / Q000175:diagnosis / Q000453:epidemiology* / Q000523:psychology; D019371:Topography, Medical