A study of plasma free amino acid levels. VIII. The relationship between plasma amino acid levels and I.Q. test performance

Abstract Fasting plasma free amino acid levels and standardized I.Q. scores for children participating in the Fels Longitudinal Study of growth and development were examined for possible relationships. Two partial replication samples were formed. One sample was composed of the first amino acid analysis made for a subject and the I.Q. score obtained nearest to it in time; the second sample consisted of the last analysis and the I.Q. test nearest to it. After age was linearly regressed from the amino acid levels, there were nontrivial correlations between amino acid level and I.Q. in both samples only in the case of tryptophan for boys and glycine for girls.