THE EFFECT ON AGGRESSION AND MOOD OF ALTERING TRYPTOPHAN LEVELS

Abstract

Summary Low levels of 5-hydroxyindoleacetic acid (5- HIAA) in the cerebrospinal fluid (CSF), indicat- ing low brain 5-hydroxytryptamine (5-HT), are found in patients with pathological aggression and also in some depressed patients, particu- larly those who attempt suicide. The associa- tion between low brain 5-HT and depression or aggression (directed toward others or self-dir- ected) is not a direct causal one because some asymptomatic people also have low CSF 5- HIAA. When the dietary amino acid and 5-HT precursor, tryptophan, is given to patients to increase 5-HT synthesis, there is no therapeu- tic effect in most severely depressed patients. However, tryptophan has some therapeutic ef- fect in manic patients. A preliminary study sug- gests a useful clinical action in pathological aggression. When a tryptophandeficient amino acid mixture is given to normal males in order 120 NUTRITION REVIEWS/SUPPLEMENT/MAY 1986 to cause an acute lowering of tryptophan and 5-HT, there is an acute lowering of mood but no effect on aggression. These data suggest that brain 5-HT, and thus tryptophan availabil- ity, may play some role in controlling mood and aggression. 5-HT seems to have an important role as a modulator of behavioral inhibition in the control of aggression, but other factors must be present to cause aggression before alterations in 5-HT have any effect. 5-HT seems to be one of many factors that can have a direct influence on mood. Acute or chronic dietary intake can alter brain tryptophan and 5-HT, but it is not known whether these changes can alter mood or aggression in any clinically significant way.