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


METHODS
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 alpha-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 alpha-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).


CONCLUSIONS
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.
Markus
C Rob
CR
Department of Experimental Psychology and the Biomedical Center, University of Maastricht, Maastricht, Netherlands. r.markus@psychology.unimaas.nl
Jonkman
Lisa M
LM
Lammers
Jan H C M
JH
Deutz
Nicolaas E P
NE
Messer
Marielle H
MH
Rigtering
Nienke
N
D000328:Adult; D000596:Amino Acids / Q000008:administration & dosage / Q000494:pharmacology*; D000704:Analysis of Variance; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D004311:Double-Blind Method; D004569:Electroencephalography; D005260:Female; D006801:Humans; D007768:Lactalbumin / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D011597:Psychomotor Performance / Q000187:drug effects*; D012890:Sleep / Q000187:drug effects*; D013997:Time Factors; D014364:Tryptophan / Q000008:administration & dosage / Q000097:blood*
D000596:Amino Acids; D014364:Tryptophan; D007768:Lactalbumin