Alpha-lactalbumin
Also called α-lactalbumin, A-LAC, ALAC, Bos d 4 (allergen name).
Best grade C across 12 graded outcomes Other Last checked
The short answer
From 14 sourcesAlpha-lactalbumin is a cow's-milk whey protein rich in tryptophan, the building block of serotonin. It raises the blood tryptophan ratio, and lab studies found better mood and cortisol under stress in stress-vulnerable people. Sleep results are mixed: a review found 5 of 8 studies positive, mainly faster sleep onset, but most recent athlete trials at 40 g were neutral.
Every graded outcome on this page
12 rows · line = participants- CGrade CSleep onset and sleep qualitySleepn 8
- DGrade DMood and cortisol under acute stressStressn 58
- DGrade DMemory scanning in stress-vulnerable adultsMemoryn 52
- DGrade DMorning alertness and attention after evening intakeAlertnessn 28
- DGrade DSleep and recovery in elite female athletes (wearable-measured)Sleepn 21
- DGrade DSleep stages and next-morning reaction time in trained people with sleep difficultiesSleepn 19
- DGrade DSleep-onset time across a competition seasonSleepn 18
- DGrade DSleep and recovery after evening competitionSleepn 16
- DGrade DForce steadiness and muscle fatigueStrengthn 16
- ∅No effectMenstruation-related symptoms and quality of lifeMenstrual symptomsn 125
- ∅No effectHabitual sleep and performance in athletes with sleep difficultiesSleepn 24
- ∅No effectSleep quality and 4-km time trial in cyclistsSleepn 12
- 9 more graded outcomes, in the evidence chapter
Key facts
- Tryptophan ratio
- 48% higher after an alpha-lactalbumin diet than after casein; 130% higher before bed after evening intake13
- Sleep review
- 5 of 8 studies positive, mainly for falling asleep faster; doses 20–60 g4
- Recent athlete trials
- 40 g nightly did not improve sleep in athletes with sleep difficulties (7 nights) or in elite female athletes (3 nights); smaller trials saw faster sleep onset or shifted sleep stages5111312
- Fatigue signal
- 40 g increased fatigue during sustained contractions in 16 adults9
- Allergen
- A major cow's-milk allergen (Bos d 4)10
What it is
Alpha-lactalbumin is a tryptophan-rich whey protein from milk, studied for sleep, mood and stress.
How it works
ProposedForms
Form
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Alpha-lactalbumin-enriched whey protein (powder) | Varies1Not applicable (whole compound or extract; no elemental fraction) | Raises the plasma tryptophan ratio within hours of a meal; a hydrolysed protein source raised it faster than intact alpha-lactalbumin.18 | 40 g doses were used in several crossover trials; one found more fatigue during sustained muscle contractions.59 | Sleep, mood under stress, morning alertness |
What the human research says
Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.
Trial map
12 graded outcomes, largest study first12 graded outcomes: 5 improved, 2 mixed, 4 no effect, 1 worsened. The largest, a 2026 randomized trial of 125 people on Menstruation-related symptoms and quality of life, found no effect. One outcome found a worsening: force steadiness and muscle fatigue (16 people).
1Menstruation-related symptoms and quality of life
No effect · No-effect grade · RCT, 125 people, 2026
Healthy Japanese women aged 20–39
Dose, result and source| Outcome | Found | People | Study | Who was studied |
|---|---|---|---|---|
| Menstruation-related symptoms and quality of life | No effect | 125 | No-effect grade · RCT, 2026 | Healthy Japanese women aged 20–39 |
| Mood and cortisol under acute stress | Improved | 58 | Grade D · RCT, 2000 | 29 highly stress-vulnerable and 29 less vulnerable adults |
| Memory scanning in stress-vulnerable adults | Mixed | 52 | Grade D · Crossover RCT, 2002 | 23 high and 29 low stress-vulnerable adults |
| Morning alertness and attention after evening intake | Improved | 28 | Grade D · Crossover RCT, 2005 | Healthy adults with or without mild sleep complaints |
| Habitual sleep and performance in athletes with sleep difficulties | No effect | 24 | No-effect grade · Crossover RCT, 2025 | Athletically trained people with sleep difficulties |
| Sleep and recovery in elite female athletes (wearable-measured) | No effect | 21 | Grade D · Crossover RCT, 2026 | NCAA Division I female athletes aged 18–25 |
| Sleep stages and next-morning reaction time in trained people with sleep difficulties | Improved | 19 | Grade D · Crossover RCT, 2025 | Trained adults with sleep difficulties |
| Sleep-onset time across a competition season | Improved | 18 | Grade D · RCT, 2023 | Semi-professional female rugby union players |
| Force steadiness and muscle fatigue | Worsened | 16 | Grade D · Crossover RCT, 2023 | Healthy adults |
| Sleep and recovery after evening competition | Improved | 16 | Grade D · Crossover RCT, 2021 | Trained women |
| Sleep quality and 4-km time trial in cyclists | No effect | 12 | No-effect grade · Crossover RCT, 2020 | Trained cyclists in two small studies (6 each) |
| Sleep onset and sleep quality | Mixed | 8 | Grade C · Systematic review, 2024 | 8 studies in adults (4 in athletes, 4 in healthy people) |
Every graded row
12 rowsShowing 12 of 12 outcomes. Human trials only.
CGrade CSleep onset and sleep qualitySleepMixedSystematic review · 8 studies
n 8 · 2024
Mixed Five of eight studies found a positive association with sleep, mainly shorter sleep-onset latency after evening intake; none found a negative effect.
- Design
- Systematic review, 8 studies, n = 8, 2024
- Population
- 8 studies in adults (4 in athletes, 4 in healthy people)
- Form
- Alpha-lactalbumin
- Dose
- 20–60 g, usually in the evening
- Duration
- Single nights to several nights
- Source
- Reference 4 · PubMed 38185736 (opens PubMed)
DGrade DMood and cortisol under acute stressStressImprovedRCT
n 58 · 2000
Improved The plasma tryptophan ratio was 48% higher. In stress-vulnerable people, cortisol fell and depressive feelings under stress were lower; effects were not reported for the less vulnerable group.
- Design
- RCT, n = 58, 2000
- Population
- 29 highly stress-vulnerable and 29 less vulnerable adults
- Form
- Diet enriched with alpha-lactalbumin vs casein
- Dose
- Not stated in the abstract
- Duration
- Single test day
- Source
- Reference 1 · PubMed 10837296 (opens PubMed)
DGrade DMemory scanning in stress-vulnerable adultsMemoryMixedCrossover RCT
n 52 · 2002
Mixed Memory scanning improved only in the high stress-vulnerable group (p = 0.019).
- Design
- Crossover RCT, n = 52, 2002
- Population
- 23 high and 29 low stress-vulnerable adults
- Form
- Diet enriched with alpha-lactalbumin vs casein
- Dose
- Not stated in the abstract
- Duration
- Single test days
- Source
- Reference 2 · PubMed 12036812 (opens PubMed)
DGrade DMorning alertness and attention after evening intakeAlertnessImprovedCrossover RCT
n 28 · 2005
Improved The tryptophan ratio rose 130% before bed; morning sleepiness fell modestly and brain measures of sustained attention improved. Behavioural performance improved only in poor sleepers.
- Design
- Crossover RCT, n = 28, 2005
- Population
- Healthy adults with or without mild sleep complaints
- Form
- Evening alpha-lactalbumin (4.8 g tryptophan per 100 g protein) vs low-tryptophan protein
- Dose
- Not stated in the abstract
- Duration
- Single nights
- Source
- Reference 3 · PubMed 15883425 (opens PubMed)
DGrade DSleep and recovery in elite female athletes (wearable-measured)SleepNo effectCrossover RCT
n 21 · 2026
No effect No condition changed total sleep time, sleep-onset latency, sleep efficiency, resting heart rate, heart rate variability, or subjective sleep and recovery compared with placebo.
- Design
- Crossover RCT, n = 21, 2026
- Population
- NCAA Division I female athletes aged 18–25
- Form
- Alpha-lactalbumin protein vs casein, carbohydrate and a 5-kcal placebo, about 30 minutes before bed
- Dose
- 40 g/night
- Duration
- 3 consecutive nights per condition
- Source
- Reference 11 · PubMed 42897977 (opens PubMed)
DGrade DSleep stages and next-morning reaction time in trained people with sleep difficultiesSleepImprovedCrossover RCT
n 19 · 2025
Improved Plasma tryptophan rose; stage 2 non-REM sleep increased (216.5 vs 205.9 min) and REM sleep decreased (99.7 vs 110.8 min), and morning reaction time improved on several cognitive tests (p<0.05).
- Design
- Crossover RCT, n = 19, 2025
- Population
- Trained adults with sleep difficulties
- Form
- Alpha-lactalbumin vs control, 2 hours before sleep
- Dose
- 40 g/night
- Duration
- 3 consecutive nights per condition
- Source
- Reference 12 · PubMed 39832504 (opens PubMed)
DGrade DSleep-onset time across a competition seasonSleepImprovedRCT
n 18 · 2023
Improved Sleep-onset latency fell in the alpha-lactalbumin group in the bye week (23.3 to 11.6 min) and away-game week (to 17.0 min) but not in the home-game week; it stayed unchanged on placebo. The abstract reports a significant effect only for sleep-onset latency.
- Design
- RCT, n = 18, 2023
- Population
- Semi-professional female rugby union players
- Form
- Alpha-lactalbumin drink vs whey protein placebo drink, 2 hours before bed
- Dose
- 40 g/night
- Duration
- Nightly through a season; sleep measured in four 7-day blocks
- Source
- Reference 13 · PubMed 37077794 (opens PubMed)
DGrade DSleep and recovery after evening competitionSleepImprovedCrossover RCT
n 16 · 2021
Improved Stage 2 non-REM sleep rose after alpha-lactalbumin but fell after the controls, and Yo-Yo test distance improved over 24 hours compared with both controls.
- Design
- Crossover RCT, n = 16, 2021
- Population
- Trained women
- Form
- Alpha-lactalbumin whey protein vs whey placebo vs water
- Dose
- One beverage after evening competition (dose not stated in the abstract)
- Duration
- Single nights
- Source
- Reference 6 · PubMed 34649262 (opens PubMed)
DGrade DForce steadiness and muscle fatigueStrengthWorsenedCrossover RCT
n 16 · 2023
Worsened Force steadiness fell by 25% during a sustained handgrip and total torque during a fatigue protocol fell 15%; maximal strength, mood and cognition did not change.
- Design
- Crossover RCT, n = 16, 2023
- Population
- Healthy adults
- Form
- Alpha-lactalbumin vs zein protein vs corn-starch drink
- Dose
- 40 g
- Duration
- Single sessions, tested 90 minutes later
- Source
- Reference 9 · PubMed 36443490 (opens PubMed)
∅No effectMenstruation-related symptoms and quality of lifeMenstrual symptomsNo effectRCT
n 125 · 2026
No effect The primary outcome, total Menstrual Distress Questionnaire score, did not differ from placebo before or during menstruation. In exploratory analyses, two premenstrual sub-scores and premenstrual role and social quality-of-life scores improved.
- Design
- RCT, n = 125, 2026
- Population
- Healthy Japanese women aged 20–39
- Form
- Alpha-lactalbumin vs placebo
- Dose
- 900 mg/day
- Duration
- Three menstrual cycles
- Source
- Reference 14 · PubMed 42568433 (opens PubMed)
∅No effectHabitual sleep and performance in athletes with sleep difficultiesSleepNo effectCrossover RCT
n 24 · 2025
No effect Awakenings rose slightly (11.0 vs 10.3), jump height fell slightly, and evening negative emotions fell; the authors conclude it may not improve sleep or performance.
- Design
- Crossover RCT, n = 24, 2025
- Population
- Athletically trained people with sleep difficulties
- Form
- Alpha-lactalbumin versus control, 2 hours before sleep
- Dose
- 40 g/night
- Duration
- 7 nights
- Source
- Reference 5 · PubMed 40218954 (opens PubMed)
∅No effectSleep quality and 4-km time trial in cyclistsSleepNo effectCrossover RCT
n 12 · 2020
No effect No differences in time in bed, total sleep time, sleep efficiency or time-trial performance.
- Design
- Crossover RCT, n = 12, 2020
- Population
- Trained cyclists in two small studies (6 each)
- Form
- Alpha-lactalbumin vs collagen peptide control, 2 hours before sleep
- Dose
- 40 g
- Duration
- 1–3 evenings
- Source
- Reference 7 · PubMed 32698123 (opens PubMed)
What the numbers add up to
Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.
Works best in people under strain
Newer sleep trials are less positive
Studied doses
Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.
Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.
Doses studied in human trials
Interactions and safety
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Interactions
0 agentsNone found in our sources.
Check with what you take
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Add a supplement or medicine you take to check it against Alpha-lactalbumin.
Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.
Who should be careful
3 groups- Cow's-milk allergy
- Alpha-lactalbumin (Bos d 4) is one of the major cow's-milk allergens.10
- Athletes before endurance or strength work
- A 40 g dose increased fatigue during sustained contractions and reduced jump height slightly in separate trials.95
- Pregnancy, breastfeeding and children
- Supplement trials cited here enrolled adults only.4
Safety notes
2 notesHow to read the label
What to check on the Supplement Facts panel.
How to read the label
2 checksFrequently asked questions
Short answers to common questions; the numbers link to the sources below.
Common questions
7 answersDoes alpha-lactalbumin help athletes sleep?
Does alpha-lactalbumin help sleep?
Does alpha-lactalbumin reduce stress?
In stress-vulnerable adults, an enriched diet lowered cortisol and depressive feelings during a lab stressor.1
Does alpha-lactalbumin help PMS or period symptoms?
Not on the main measure. In a 2026 trial in 140 women, 900 mg/day for three cycles did not change overall menstrual distress scores versus placebo; only some secondary quality-of-life scores improved.14
What are the side effects of alpha-lactalbumin?
Is it better than tryptophan?
A hydrolysed protein raised blood tryptophan availability more than intact alpha-lactalbumin or pure tryptophan in one study.8
Sources
14 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.
Sources cited on this page
14 sources- 1The bovine protein alpha-lactalbumin increases the plasma ratio of tryptophan to the other large neutral amino acids, and in vulnerable subjects raises brain serotonin activity, reduces cortisol concentration, and improves mood under stress.RCT Am J Clin Nutr, 2000 · PMID 10837296
- 2Whey protein rich in alpha-lactalbumin increases the ratio of plasma tryptophan to the sum of the other large neutral amino acids and improves cognitive performance in stress-vulnerable subjects.Crossover RCT Am J Clin Nutr, 2002 · PMID 12036812
- 3Evening intake of alpha-lactalbumin increases plasma tryptophan availability and improves morning alertness and brain measures of attention.Crossover RCT Am J Clin Nutr, 2005 · PMID 15883425
- 4Alpha-lactalbumin and sleep: A systematic review.Systematic review J Sleep Res, 2024 · PMID 38185736
- 5Pre-Sleep Alpha-Lactalbumin Supplementation Does Not Improve the Habitual Sleep and Performance of Sportspeople with Sleep Difficulties.Crossover RCT Nutrients, 2025 · PMID 40218954
- 6ɑ-Lactalbumin Improves Sleep and Recovery after Simulated Evening Competition in Female Athletes.Crossover RCT Med Sci Sports Exerc, 2021 · PMID 34649262
- 7Presleep α-Lactalbumin Consumption Does Not Improve Sleep Quality or Time-Trial Performance in Cyclists.Crossover RCT Int J Sport Nutr Exerc Metab, 2020 · PMID 32698123
- 8Effect of different tryptophan sources on amino acids availability to the brain and mood in healthy volunteers.Crossover RCT Psychopharmacology (Berl), 2008 · PMID 18648776
- 9Effects of α-lactalbumin on strength, fatigue and psychological parameters: a randomised double-blind cross-over study.Crossover RCT Eur J Appl Physiol, 2023 · PMID 36443490
- 10Research progress on the characteristics of milk allergens and the effect of Maillard reaction and its assistance treatment on allergenicity.Review Food Chem, 2026 · PMID 42056772
- 11Pre-sleep milk-derived proteins do not impair sleep or recovery in elite female athletes.Crossover RCT J Int Soc Sports Nutr, 2026 · PMID 42897977
- 12Evening Alpha-Lactalbumin Supplementation Alters Sleep Architecture and Reduces Morning Reaction Time in an Athletically Trained Population With Sleep Difficulties.Crossover RCT Int J Sport Nutr Exerc Metab, 2025 · PMID 39832504
- 13The effect of α-lactalbumin consumption on sleep quality and quantity in female rugby union athletes: a field-based study.RCT Biol Sport, 2023 · PMID 37077794
- 14Effect of long-term intake of α-lactalbumin on menstruation-related symptoms and quality of life in healthy Japanese women: a randomized, double-blind, placebo-controlled study.RCT Front Nutr, 2026 · PMID 42568433
What changed
Every dated change to this page: what changed, who made it and why.
Change log
3 entries| Date | Change | Who and why |
|---|---|---|
| evidence, studied doses, FAQ, questions | Added three sleep trials (2026 elite female athletes, no effect; 2025 sleep-architecture crossover; 2023 rugby season study) and the 2026 menstrual-symptom RCT (900 mg/day, primary outcome null). Replaced three FAQ items (one duplicated an auto-derived question) with athlete sleep, timing and side effects, added a PMS item, three page questions and sleep and stress goal-hub links; updated key facts and studied doses. Interactions re-checked: no LactMed or LiverTox entry and no published drug interaction found; the list stays empty. | Writer: Kymata Health EditorialTrigger: A–Z audit against docs/supplements/AUDIT-STANDARD.md |
| Evidence | Corrected the study design on: Morning alertness and attention after evening intake. Each participant slept two lab nights, one after each test diet, so the trial is a crossover. | Writer: Kymata Health EditorialTrigger: Correction |
| all | Initial editorial evidence review (first draft). Every PMID checked against NCBI E-utilities esummary (titles and years taken from the record) and the abstract read for each cited row. Studied doses are reported as research doses, not dosing advice. | Writer: Kymata Health EditorialTrigger: new page |
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