Soy peptide dietary supplementation increases serum dopamine level and improves cognitive dysfunction in subjects with mild cognitive impairment

The intake of soy peptide preparations composed mainly of di－ and tri－peptides（Hinute, Fuji Oil Co.）is reported to modulate the levels of certain neuroactive amino acids in the adult mouse brain. The present study examined the effects of soy peptide supplementation on higher brain function. The subjects were 30 patients with mild cognitive impairment（soy peptide group：mean age：58.1±1.7 years, n＝15, placebo group：58.9±1.8 years, n＝15）.Cognitive function was evaluated by the Japanese version of repeatable battery for the assessment of neuropsychological states（RBANS）at two time points：at baseline and after 8－week dietary supplementation of 8 g／day soy peptides or placebo. Soy peptide supplementation significantly improved the delayed memory score and tended to improve immediate memory （score of story memory）, compared with placebo. In addition, soy peptide intake significantly increased serum dopamine, which is associated with memory function, compared with the placebo. The results suggest that soy peptide supplementation can improve aging－related cognitive dysfunction.