Seasonal variations in mood and behaviour: epidemiological findings in the north tropics.

BACKGROUND: There has been no epidemiological study of seasonal affective disorder (SAD) in the north tropics. METHODS: The investigators randomly mailed the Seasonal Pattern Assessment Questionnaire (SPAQ) to 520 residents in Chiang Mai Municipality. RESULTS: The prevalence rates of summer SAD, subsyndromal summer SAD and winter SAD are 6.19%, 8.25% and 1.03%, respectively. CONCLUSIONS: The epidemiological study of SAD in the north tropics finds a high prevalence of summer SAD, low prevalence of winter SAD and the correlation between 'feel worst' response and temperature. LIMITATIONS: The reliability and validity of SPAQ in diagnosing summer SAD is probably low. The response rate from the studied sample is low. CLINICAL RELEVANCE: The prevalence of summer SAD in the tropics is much higher than that in the temperate zone and may relate to temperature.