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Aggression, Serotonin, and Seasonality

To the Editor: Barbara Stanley, Ph.D., and colleagues (1) reported decreased concentrations of 5-hydroxyindoleacetic acid (5-HIAA) in CSF in a cohort of aggressive and nonaggressive patients without the "potential confound" of suicidal behavior. However, the authors did not acknowledge the important potential confound of seasonal variation in both serotonin function and aggressive behavior. Significant seasonal variation in CSF 5-HIAA concentrations in healthy humans has been reported (2). A review of studies demonstrating significant seasonal variation in a variety of measures of serotonin function in humans has been published elsewhere (3). This fluctuation may underlie the seasonal variation seen in a number of psychiatric disorders and phenomena, including suicide. Notably, the prevalence of human aggression has been shown to vary significantly across seasons (4, 5).

Therefore, given that the role of seasonality in this study was not analyzed by the authors, their conclusions about possible links between CSF 5-HIAA concentrations and aggression may be premature. Seasonal differences in time of lumbar punctures could explain any group differences the authors found. A seasonal analysis could be accomplished by performing a two-way analysis of variance by using the presence of aggression and season as independent variables. Another approach would be to use season or even photoperiod as covariates in an analysis of covariance. Arguably, ample evidence now mandates that seasonality be controlled in all studies of serotonin function.

References

1. Stanley B, Molcho A, Stanley M, Winchel R, Gameroff MJ, Parsons B, Mann JJ: Association of aggressive behavior with altered serotonergic function in patients who are not suicidal. Am J Psychiatry 2000; 157:609-614[Abstract/Free Full Text]
2. Brewerton TD, Berrettini WH, Nurnburger JI Jr, Linnoila M: Analysis of seasonal fluctuations of CSF monoamine metabolites and neuropeptides in normal controls: findings with 5HIAA and HVA. Psychiatry Res 1988; 23:257-265[CrossRef][Medline]
3. Brewerton TD: Seasonal variation of serotonin function in humans: research and clinical implications. Ann Clin Psychiatry 1989; 1:153-164[Medline]
4. Michael RP, Zumpe D: Sexual violence in the United States and the role of season. Am J Psychiatry 1983; 140:883-886[Abstract/Free Full Text]
5. Michael RP, Zumpe D: An annual rhythm in the battering of women. Am J Psychiatry 1986; 143:637-640[Abstract/Free Full Text]

Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Email this article to a Colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to My Articles & Searches Download to citation manager Citing Articles via Google Scholar Articles by BREWERTON, T. D. Search for Related Content PubMed Citation Articles by BREWERTON, T. D. Neurotransmitters Seasonal Affective Disorder Other Violence/Aggression

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