Global prevalence of seasonal affective disorder by latitude: A systematic review and meta-analysis

Background: Seasonal affective disorder (SAD) has been reported globally, yet no comprehensive meta-analysis has systematically examined the association between latitude and SAD prevalence. This study aimed to investigate the relationship between latitude and the prevalence of SAD, subsyndromal SAD (SSAD), and summer-type SAD. Methods: A systematic search was conducted in Medline, Embase, Web of Science, Scopus, and ScienceDirect on May 23, 2025. Eligible studies were cross-sectional and used the Seasonal Pattern Assessment Questionnaire (SPAQ) to diagnose SAD. Data were extracted on prevalence, latitude, age, sex, region, income level, and Koppen climate zones. Pooled prevalence rates were calculated using a random-effects model. Meta-regression and subgroup analyses were performed to assess the influence of latitude and other moderators. Results: Twenty-four studies with 32,866 participants were included. The pooled prevalence of SAD was 5.01% [4.15-5.86], SSAD was 9.37% [7.55-11.18], and summer-type SAD was 0.57% [0.36-0.79]. Meta-regression revealed a significant positive association between latitude and both SAD ((3 = 0.2, p < 0.001) and SSAD ((3 = 0.32, p < 0.001). No such association was found for summer-type SAD. Conclusion: This meta-analysis provides quantitative evidence that higher latitude is significantly associated with increased prevalence of SAD and SSAD. These findings underscore the potential role of seasonal light variation in the pathogenesis of winter-pattern depressive disorders.