Evening intake of α-lactalbumin increases plasma tryptophan availability and improves morning alertness and brain measures of attention
Open accessAbstract
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.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 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).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.
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In healthy adults (n = 14) with sleep complaints, evening ingestion of α-lactalbumin (20 g) resulted in a 130% increase in tryptophan:LNAA prior to bed and a modest but significant reduction in morning sleepiness and improved alertness the following morning.
“In a similar study, healthy adults (n = 14) with sleep complaints consumed milkshakes containing either α-lactalbumin (20 g) or a casein placebo. Evening ingestion of α-lactalbumin resulted in a 130% increase in tryptophan:LNAA prior to bed and modest but significant reduction in morning sleepiness and improved alertness the following morning [55].”
From Sleep and Nutrition Interactions: Implications for Athletes (2019) · cites this paper as [55]
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References 46 · Cited by 157
Research works printed but not linked: 7
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- Authors
- Markus, C. R., Jonkman, L. M., Lammers, J. H., Deutz, N. E., Messer, M. H., & Rigtering, N.
- Affiliations
- Maastricht University (NL)
- Corresponding author
- Markus, C Rob
- Venue
- The American Journal of Clinical Nutrition
- Publisher
- Elsevier BV
- Published
- 2005-05
- Volume
- 81
- Issue
- 5
- Pages
- 1026-1033
- ISSN
- 0002-9165 (ISSN-L)
- OpenAlex
- W1942982649
- Cited by
- 157
- References
- 46
- Citations by year
- 2026: 4 · 2025: 7 · 2024: 8 · 2023: 13 · 2022: 4 · 2021: 9 · 2020: 15 · 2019: 6 · 2018: 6 · 2017: 10 · 2016: 7 · 2015: 7 · 2014: 3 · 2013: 5 · 2012: 11
- FWCI
- 1.90
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Licence
- Locations
- American Journal of Clinical Nutrition (publishedVersion)
- PubMed (publishedVersion)
- Research Publications (Maastricht University) (acceptedVersion, other-oa)
- TNO Repository (submittedVersion)
- Repository hosted by TU Delft Library (TU Delft) (submittedVersion)
- Data Archiving and Networked Services (DANS) (submittedVersion)
- Research Publications (Maastricht University) (submittedVersion, other-oa)
- Topics
- Life Sciences › Neuroscience › Biological Psychiatry › Tryptophan and brain disorders
- Life Sciences › Neuroscience › Cognitive Neuroscience › Sleep and Wakefulness Research
- Social Sciences › Psychology › Experimental and Cognitive Psychology › Sleep and Work-Related Fatigue
- Keywords
- alpha-lactalbumin, tryptophan availability, serotonin precursor, sleep complaints, sustained attention, sleepiness, continuous performance test, large neutral amino acids, sleep quality
- MeSH terms
- Adult, Amino Acids, Analysis of Variance, Brain, Double-Blind Method, Electroencephalography, Female, Humans, Lactalbumin, Male, Psychomotor Performance, Sleep, Time Factors, Tryptophan
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