The relation of free plasma tryptophan to anger, hostility, and aggression in a nonpatient sample of adult men and women

Background: Dysregulation of central nervous system serotonergic (5-HT) activity is implicated in behavioral states and psychological traits associated with depression and aggression, with some studies suggesting possible gender-related differences. Purpose: This study examined the relation of free plasma tryptophan (TRP) to aggression and depression in a sample of 138 nonsmoking adults recruited from the general community. It was hypothesized that TRP would be associated with anger hostility, and aggression. Methods: To minimize effects of diurnal variation and menstrual cycle, fasting blood samples were collected in the morning, and, for women, during the follicular phase of the menstrual cycle. Participants were administered questionnaires following blood draw. Plasma TRP was determined by high performance liquid chromatography. Results: In women, but not men, higher levels of TRP were associated with trait hostility, propensity for anger, a tendency to express anger outwardly, and an antagonistic interpersonal style. For men and women, greater severity of depressive symptoms, anger and the verbal expression of anger were associated with higher TRP. These associations were independent of age, body mass index, fasting albumin, and race and ethnicity. Conclusions: These data suggest that in women, but not men, higher plasma levels of TRP the precursor to 5-HT are associated with anger-hostility-aggression and that these associations are independent of various potential confounds. Implications of these observations to studies employing acute TRP depletion studies are discussed.