Seasonal variations in internalizing, externalizing, and substance use disorders in youth.

Seasonal variations were assessed in symptoms of internalizing (anxiety and mood), externalizing (attention-deficit/hyperactivity and oppositional defiant disorders), and substance use disorders in youth. This study is based on secondary data analysis of two NIMH-funded epidemiologic-services studies: (a) Alternative Service Use Patterns by Youth with Serious Emotional Disturbance (N=936, ages 9-17); and (b) Methods for the Epidemiology of Child and Adolescent Mental Disorders (N=1285, ages 9-17). Child psychiatric diagnoses were measured by the Diagnostic Interview Schedule for Children. Variables that indicate site of the interview and service system, as well as age, gender, and ethnicity, were used as covariates. Significant annual variations were found in symptom counts of overanxious disorder, obsessive-compulsive disorder, separation anxiety disorder, social phobia, and major depressive disorder, with the estimated nadir in August-October. There may be weak seasonal variations in attention-deficit/hyperactivity disorder with estimated nadir in August, oppositional defiant disorder with estimated nadir in August-September, and marijuana use with estimated zenith in August-September. Significant seasonality in alcohol, other substance use, agoraphobia, and panic disorder was not found. There may be an instrument-specific bias in estimated nadir. Real nadirs may be up to 3 months prior to the estimated nadirs specified above. Findings suggest that seasonality in symptoms should be considered when assessment instruments of childhood psychiatric disorders are developed, as well as when epidemiological and clinical data are collected and analyzed.