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Evening intake of α-lactalbumin increases plasma tryptophan availability and improves morning alertness and brain measures of attention

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Author: Markus, C.R. · Jonkman, L.M. · Lammers, J.H.C.M. · Deutz, N.E.P. · Messer, M.H. · Rigtering, N.
Type:article
Date:2005
Institution: TNO Kwaliteit van Leven TNO Voeding
Source:American Journal of Clinical Nutrition, 5, 81, 1026-1033
Identifier: 239025
Keywords: Biology Toxicology · Toxicology and Applied Pharmacology · α-lactalbumin · Attention · Continuous performance task · Event-related brain acivity · Sleep complaints · Tryptophan · Alpha lactalbumin · Placebo · Tryptophan · Amino acid · Lactalbumin · Adult · Alertness · Brain function · Clinical trial · Controlled clinical trial · Controlled study · Diet · Double blind procedure · Drug effect · Female · Human · Male · Reaction time · Somnolence · Task performance · Analysis of variance · Blood · Brain · Electroencephalography · Metabolism · Psychomotor performance · Sleep · Time · Adult · Amino Acids · Analysis of Variance · Brain · Double-Blind Method · Electroencephalography · Female · Humans · Lactalbumin · Male · Psychomotor Performance · Sleep · Time Factors · Tryptophan

Abstract

Background: Brain serotonin function is thought to promote sleep regulation and cognitive processes, whereas sleep abnormalities and subsequent behavioral decline are often attributed to deficient brain serotonin activity. Brain uptake of the serotonin precursor tryptophan is dependent on nutrients that influence the availability of tryptophan via a change in the ratio of plasma tryptophan to the sum of the other large neutral amino acids (Trp:LNAA). Objective: We tested whether evening consumption of α-lactalbumin protein with an enriched tryptophan content of 4.8 g/100 g increases plasma Trp:LNAA and improves alertness and performance on the morning after sleep, particularly in subjects with sleep complaints. Design: Healthy subjects with (n = 14) or without (n = 14) mild sleep complaints participated in a double-blind, placebo-controlled study. The subjects slept at the laboratory for 2 separate nights so that morning performance could be evaluated after an evening diet containing either tryptophan-rich α-lactalbumin or tryptophan-low placebo protein. Evening dietary changes in plasma Trp:LNAA were measured. Behavioral (reaction time and errors) and brain measures of attention were recorded during a continuous performance task. Results: Evening α-lactalbumin intake caused a 130% increase in Trp:LNAA before bedtime (P = 0.0001) and modestly but significantly reduced sleepiness (P = 0.013) and improved brain-sustained attention processes (P = 0.002) the following morning. Only in poor sleepers was this accompanied by improved behavioral performance (P = 0.05). Conclusion: Evening dietary increases in plasma tryptophan availability for uptake into the brain enhance sustained alertness early in the morning after an overnight sleep, most likely because of improved sleep. © 2005 American Society for Clinical Nutrition.