|Vol. 4, No. 2, 1998 Page 1|
Research implicates abnormal levels of the neurotransmitter serotonin as a risk factor for aggressive behavior, but most studies have involved only small numbers of clinical subjects. Now, however, a large epidemiological study offers strong evidence linking abnormal serotonin levels to aggression.
Terrie Moffitt and colleagues studied the blood serotonin levels of 781 21-year-old men and women. The criminal histories of subjects were determined both from self-reports and from records of court convictions.
The researchers report that "in this study, elevated whole blood serotonin was characteristic of violent men." (Low brain levels of serotonin, but high levels of blood serotonin, are associated with behavior disorders-apparently because of serotonin's different origin and function in blood and brain.) The violent men's mean serotonin level was .48 standard deviations (SD) above the norm for males as a group, and .56 SD above the mean for non-violent men. Among female subjects, no relationship between serotonin levels and aggression was seen.
"To our knowledge," Moffitt and colleagues say, "this is the first study to demonstrate that a possible index of serotonergic function is related to violence in the general population." Moreover, they say, "the epidemiological serotonin effect was not small, [but rather] indicated a moderate effect size in the population." They note that the finding "was specific to violence, as opposed to general crime," and it was significant whether self-reported aggression or court records of aggression were considered.
Furthermore, Moffitt et al. say, the effects of elevated blood serotonin on aggression remained significant after the researchers controlled for a host of factors including gender, diurnal variation, diet, psychiatric medications, illicit drug use, season during which the blood test was done, plasma levels of tryptophan (the dietary precursor of serotonin), alcohol and tobacco use, psychiatric diagnoses, platelet count, body mass, socioeconomic status, IQ, and history of suicide attempts.
"Whole blood serotonin relates to violence in an epidemiological study," Terrie E. Moffitt, Gary L. Brammer, Avshalom Caspi, J. Paul Fawcett, Michael Raleigh, Arthur Yuwiler, and Phil Silva, Biological Psychiatry, Vol. 43, No. 6, March 15, 1998, pp. 446-457. Address: Terrie E. Moffitt, Institute of Psychiatry, 111 Denmark Hill, London SE5 8AF, UK.