The consumption of a specifically prepared silk fibroin protein enzymatic hydrolysate (FPEH) has been reported to improve cognitive function in healthy humans. The objective of the current study is to evaluate the dose-dependent effects of the FPEH on memory. Healthy adults with an average age of approximately 55 years were administered doses of 0, 280, 400 and 600 mg of FPEH per day in two divided doses for 3 weeks. The Rey–Kim Auditory Verbal Learning Test and the Rey–Kim Complex Figure Test of the Rey–Kim Memory Test were used to evaluate memory at baseline and after 3 weeks. The scores for each test were combined into the memory quotient score (MQ). Learning gradient, memory maintenance, retrieval efficacy, and drawing/recall scores were also compared. After 3 weeks of FPEH, dose-dependent increases were observed for the MQ, the learning gradient, the numbers of words remembered, the retrieval efficiency, and drawing/recall. The optimal dose for FPEH was 400 or 600 mg, depending on the end point measured. No adverse effects were reported. FPEH significantly improved measurements of memory in healthy adults by 3 weeks at doses over 280 mg daily, with an apparent plateau effect at 400–600 mg daily.
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