Limited evidenceSleep & relaxation

Alpha-Lactalbumin

A whey protein fraction unusually rich in tryptophan, taken in the evening to raise brain serotonin. The mechanism is real and measurable, but the sleep trials that followed are small and contradictory.

Evidence last reviewed: August 2026

What the science says

Tryptophan availability and morning alertness Limited evidence
The foundational trial found that evening intake of alpha-lactalbumin raised the plasma tryptophan-to-large-neutral-amino-acid ratio and improved morning alertness and brain measures of attention in poor sleepers. It was a small crossover study, and the outcome was next-morning function rather than sleep itself.
Sleep architecture in athletes Limited evidence
A randomised trial in athletically trained people with sleep difficulties found that evening alpha-lactalbumin altered sleep architecture and reduced morning reaction time. Effects were on measured sleep stages more than on how much or how well people slept.
Habitual sleep quality Limited evidence
A separate randomised trial from the same group found that pre-sleep alpha-lactalbumin did not improve habitual sleep or performance in sportspeople with sleep difficulties. Taken together, the literature is small, mixed, and confined mostly to athletes.

Dosage & safety

Studied doseTrials have used roughly 20–40 g of alpha-lactalbumin-enriched whey in the evening, typically 1–2 hours before bed. Ordinary whey protein isolate contains far less alpha-lactalbumin and is not equivalent.

SafetyA milk protein — unsuitable for anyone with milk allergy, and it contains lactose traces. Large evening protein doses can cause bloating or reflux in some people. No known drug interactions, but people on MAO inhibitors or serotonergic drugs should be cautious with large tryptophan loads. Not a treatment for chronic insomnia.

Scientific references

Evening intake of alpha-lactalbumin increases plasma tryptophan availability and improves morning alertness and brain measures of attention
Markus CR, Jonkman LM, Lammers JH — Am J Clin Nutr, 2005
Evening Alpha-Lactalbumin Supplementation Alters Sleep Architecture and Reduces Morning Reaction Time in an Athletically Trained Population With Sleep Difficulties
Barnard J, Roberts S, Lastella M — Int J Sport Nutr Exerc Metab, 2025
Pre-Sleep Alpha-Lactalbumin Supplementation Does Not Improve the Habitual Sleep and Performance of Sportspeople with Sleep Difficulties
Barnard J, Roberts S, Lastella M — Nutrients, 2025

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