Casein protein
Also called casein, micellar casein, calcium caseinate, sodium caseinate, milk protein (slow-digesting), night protein.
Best grade B across 6 graded outcomes Other Last checked
The short answer
From 12 sourcesCasein is a slow-digesting milk protein. In a 12-week trial of 44 young men, 27.5 g of protein before sleep added more thigh muscle area than placebo (+8.4 vs +4.8 cm2). In 41 older men a similar plan added nothing. A 116-trial network analysis found night protein helped strength, while total daily protein appears to matter most.
Every graded outcome on this page
6 rows · line = participants- BGrade BFat-free mass, muscle mass and strength with protein timing and typeProtein supplements of 14 types, including casein and other milk proteinsn 4,711
- CGrade CMuscle size and strength during resistance trainingProtein supplement before sleep (27.5 g protein, 15 g carbohydrate, 0.1 g fat); the abstract does not name the protein sourcen 44
- CGrade COvernight protein synthesis and training adaptationsMostly casein before sleepn 9
- DGrade DMuscle mass and strength in older menProtein supplement after exercise and before sleep (21 g protein, 3 g leucine, 9 g carbohydrate, 3 g fat); protein source not stated in the abstractn 41
- DGrade DBlood amino acid response by casein typeMicellar casein, calcium caseinate and cross-linked sodium caseinaten 15
- DGrade DLean mass and strength: daytime vs nighttime caseinCasein supplementn 13
- 3 more graded outcomes, in the evidence chapter
Key facts
- Digestion
- Casein gave a prolonged, moderate rise in blood amino acids; whey gave a short, sharp one (leucine tracer study)7
- Before sleep, young men
- 27.5 g protein nightly for 12 weeks: quadriceps area +8.4 vs +4.8 cm2 on placebo (p < 0.05)4
- Before sleep, older men
- 21 g protein after exercise and before sleep for 12 weeks: no extra muscle or strength vs placebo in 41 men6
- Timing vs total
- Daytime and nighttime casein (35 g/day) gave similar gains in 13 men eating 1.8 g/kg protein5
- Form matters
- Cross-linked sodium caseinate was digested faster than micellar casein or calcium caseinate (40 g, 15 men)8
- Allergy
- Milk is a major US food allergen; supplements containing casein must declare it12
What it is
Casein is the main protein in cow's milk, sold as micellar casein or caseinate powders that digest slowly and are often used as a bedtime protein.
How it works
EstablishedCasein clots in the stomach, which slows gastric emptying and spreads amino acid delivery over several hours. In a leucine tracer study this produced a prolonged plateau of moderate hyperaminoacidemia, a 34% fall in whole-body protein breakdown and a smaller rise in protein synthesis (+31%) than whey (+68%), with a more positive 7-hour net leucine balance.78
Forms, side by side
3 forms named in our sources. The rest show what our data holds, and say plainly where it holds nothing yet.
Casein protein forms compared
3 forms| 3 forms | Micellar casein | Calcium caseinate | Cross-linked sodium caseinate (experimental) |
|---|---|---|---|
| Absorption in people | Slowly digested; in the 40 g crossover, plasma amino acids rose more gradually than with cross-linked caseinate. Casein released amino acids into blood more slowly than whey.871 | Digested similarly to micellar casein in the 40 g crossover; its total amino acid response was lower than that of cross-linked sodium caseinate (260 vs 294).8 | More rapidly digested than micellar casein or calcium caseinate; plasma amino acids were higher from 15 to 90 minutes.8 |
| GI tolerance | No product-specific safety signal in the cited studies; the trials were short and small.48 | Not reported separately in the cited abstracts.8 | Not reported in the cited abstract.8 |
| Studied for | Bedtime protein with resistance training (27.5 to 40 g) | Amino acid kinetics in a single-dose crossover | Showing that processing changes casein digestion speed |
- Micellar casein
- Absorption in people
- Slowly digested; in the 40 g crossover, plasma amino acids rose more gradually than with cross-linked caseinate. Casein released amino acids into blood more slowly than whey.871
- GI tolerance
- No product-specific safety signal in the cited studies; the trials were short and small.48
- Studied for
- Bedtime protein with resistance training (27.5 to 40 g)
- Calcium caseinate
- Cross-linked sodium caseinate (experimental)
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
6 graded outcomes, largest study first6 graded outcomes: 2 improved, 2 mixed, 2 no effect. The largest, a 2024 meta-analysis of 4,711 people on Fat-free mass, muscle mass and strength with protein timing and type, found an improvement.
1Fat-free mass, muscle mass and strength with protein timing and type
Improved · Grade B · Meta-analysis, 4,711 people, 2024
Adults doing resistance training in 116 randomized trials
Dose, result and source| Outcome | Found | People | Study | Who was studied |
|---|---|---|---|---|
| Fat-free mass, muscle mass and strength with protein timing and type | Improved | 4,711 | Grade B · Meta-analysis, 2024 | Adults doing resistance training in 116 randomized trials |
| Muscle size and strength during resistance training | Improved | 44 | Grade C · RCT, 2015 | Healthy young men (mean age 22) in a progressive 12-week resistance program |
| Muscle mass and strength in older men | No effect | 41 | Grade D · RCT, 2018 | Active men aged about 70 in a 12-week, 3-session-a-week resistance program |
| Blood amino acid response by casein type | Mixed | 15 | Grade D · Crossover RCT, 2020 | Healthy young men (mean age 26) |
| Lean mass and strength: daytime vs nighttime casein | No effect | 13 | Grade D · RCT, 2018 | 13 men in a 10-week supervised resistance program, diets set at 1.8 g/kg protein |
| Overnight protein synthesis and training adaptations | Mixed | 9 | Grade C · Systematic review, 2021 | Young and older men across 9 included articles |
Every graded row
6 rowsShowing 6 of 6 outcomes. Human trials only.
BGrade BFat-free mass, muscle mass and strength with protein timing and typePerformanceImprovedMeta-analysis
n 4,711 · 2024
Versus placebo, protein at night improved handgrip strength by 2.85 kg and leg press by 12.12 kg; protein after exercise added 0.54 kg fat-free mass. Milk proteins, including casein, were effective for both mass and strength (moderate certainty). No timing or type improved physical-performance tests.
- Design
- Meta-analysis, n = 4,711, 2024
- Population
- Adults doing resistance training in 116 randomized trials
- Form
- Protein supplements of 14 types, including casein and other milk proteins
- Dose
- Varied by trial
- Duration
- Varied by trial
- Source
- Reference 2 · PubMed 38039960 (opens PubMed)
CGrade CMuscle size and strength during resistance trainingPerformanceImprovedRCT
n 44 · 2015
Strength gain was +164 kg vs +130 kg with placebo (p < 0.001). Quadriceps cross-sectional area rose +8.4 vs +4.8 cm2 (p < 0.05) and type II fiber size +2319 vs +1017 um2 (p < 0.05).
- Design
- RCT, n = 44, 2015
- Population
- Healthy young men (mean age 22) in a progressive 12-week resistance program
- Form
- Protein supplement before sleep (27.5 g protein, 15 g carbohydrate, 0.1 g fat); the abstract does not name the protein source
- Dose
- 27.5 g protein nightly
- Duration
- 12 weeks
- Source
- Reference 4 · PubMed 25926415 (opens PubMed)
CGrade COvernight protein synthesis and training adaptationsPerformanceMixedSystematic review · 9 studies
n 9 · 2021
20 to 40 g of casein before sleep raised overnight whole-body protein synthesis in young and older men. Training adaptations improved over 10 to 12 weeks in young but not older men. The authors caution that protein intakes were uneven between groups.
- Design
- Systematic review, 9 studies, n = 9, 2021
- Population
- Young and older men across 9 included articles
- Form
- Mostly casein before sleep
- Dose
- 20 to 40 g about 30 minutes before sleep
- Duration
- Acute overnight studies and 10 to 12 weeks of training
- Source
- Reference 3 · PubMed 32811763 (opens PubMed)
DGrade DMuscle mass and strength in older menHealthy agingNo effectRCT
n 41 · 2018
Leg-extension 1RM, quadriceps area, type II fiber size and muscle protein synthesis rate (1.57 vs 1.62%/day) did not differ from an energy-matched placebo.
- Design
- RCT, n = 41, 2018
- Population
- Active men aged about 70 in a 12-week, 3-session-a-week resistance program
- Form
- Protein supplement after exercise and before sleep (21 g protein, 3 g leucine, 9 g carbohydrate, 3 g fat); protein source not stated in the abstract
- Dose
- 21 g protein after training and nightly
- Duration
- 12 weeks
- Source
- Reference 6 · PubMed 30247714 (opens PubMed)
DGrade DBlood amino acid response by casein typePerformanceMixedCrossover RCT
n 15 · 2020
Total amino acid incremental AUC was 294 for cross-linked sodium caseinate vs 260 for calcium caseinate (p = 0.006), with micellar casein in between (270). Amino acid levels were higher with the cross-linked form from 15 to 90 minutes.
- Design
- Crossover RCT, n = 15, 2020
- Population
- Healthy young men (mean age 26)
- Form
- Micellar casein, calcium caseinate and cross-linked sodium caseinate
- Dose
- 40 g of casein protein, single dose
- Duration
- 6-hour measurement, 1-week washout
- Source
- Reference 8 · PubMed 32751788 (opens PubMed)
DGrade DLean mass and strength: daytime vs nighttime caseinPerformanceNo effectRCT
n 13 · 2018
Both timing groups gained lean soft tissue, muscle cross-sectional area and leg and bench press strength, with no difference between groups (p > 0.05).
- Design
- RCT, n = 13, 2018
- Population
- 13 men in a 10-week supervised resistance program, diets set at 1.8 g/kg protein
- Form
- Casein supplement
- Dose
- 35 g casein daily, taken earlier in the day or shortly before bed
- Duration
- 10 weeks
- Source
- Reference 5 · PubMed 29764464 (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.
The slow-digestion idea is well supported; the muscle payoff is smaller
Timing evidence is mixed
Whey ranked above casein for older adults
In a 78-trial network analysis of six protein sources in older adults doing resistance training, whey ranked most effective for muscle mass, handgrip and walking speed.10
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
NIH ODS updated Apr 1, 2024Doses studied in human trials ranged from about 20 to 40 g of casein protein per serving, usually about 30 minutes before sleep, for 10 to 12 weeks alongside resistance training; kinetics studies used single 40 g servings. These are research doses, not advice.3458
Intake reference: Protein RDA: 0.8 g/kg/day for healthy adults and 0.85 g/kg/day for adolescents. The NIH fact sheet notes that athletes may need more; it does not set an upper limit for protein.1 The Food and Nutrition Board has not set a UL for protein but advises caution with high intakes from foods plus supplements because data on adverse effects are limited. NIH ODS fact sheet (updated April 1, 2024).
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.
What Casein protein meets
1 cited rowMedicines 1
Supplements and foods 0
No supplement rows in our sources.
- Measured in a human study
Choose a medicine or supplement above to read its cited rows here.
Also cited:
Levodopa
PK studyMeasured in a human study
Levodopa, for example carbidopa-levodopa for Parkinson's disease: In nine people with Parkinson's, high-protein meals and the amino acids leucine, isoleucine or phenylalanine (100 mg/kg) reversed the effect of infused levodopa without lowering plasma levodopa, by competing for transport into the brain. The study did not test casein itself, so ask the prescriber about timing protein shakes.
Source 11, N Engl J Med (1984)
Interactions
1 agent| Agent | What the source says | Evidence |
|---|---|---|
| Medicines1 | ||
| Levodopae.g. carbidopa-levodopa for Parkinson's disease | In nine people with Parkinson's, high-protein meals and the amino acids leucine, isoleucine or phenylalanine (100 mg/kg) reversed the effect of infused levodopa without lowering plasma levodopa, by competing for transport into the brain. The study did not test casein itself, so ask the prescriber about timing protein shakes.11 | PK study |
Check with what you take
Kept on this device onlyAdd what you take. We list every interaction our evidence profiles cite between Casein protein and your picks, and between your picks.
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Add a supplement or medicine you take to check it against Casein protein.
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
5 groups- Milk allergy
- Casein is a milk protein, and milk is a major US food allergen. People with a milk allergy should avoid casein products; labels must name milk as the allergen source. Reactions range from hives to anaphylaxis.12
- Kidney disease
- A systematic review in healthy adults found protein above the RDA consistent with normal kidney function in the short term, but it excluded people with kidney disease and most studies ran under 6 months. Anyone with kidney disease should ask their care team about protein supplements.9
- Parkinson's disease on levodopa
- Dietary protein can blunt levodopa's effect; see the interaction above.11
- Older adults expecting extra muscle
- A 12-week trial in active older men found no added muscle or strength from protein after exercise and before sleep, and a network analysis in older adults ranked whey above casein.610
- Pregnancy, breastfeeding and children
- No casein supplement studies in these groups were found in the sources reviewed, so safety of concentrated supplements is unknown.1
How to read the label
What to check on the Supplement Facts panel.
How to read the label
4 checksCheck the protein grams
Look for the form
Micellar casein, calcium caseinate and sodium caseinate digest at different speeds, and cross-linked sodium caseinate was digested faster in a 40 g crossover.8
Read the allergen statement
FDA requires packaged foods and dietary supplements to declare milk, either in the ingredient list or in a 'Contains' statement.12
Count it in your daily total
In a 10-week study with intake fixed at 1.8 g/kg, casein earlier in the day worked as well as at night, so the supplement counts toward the daily total.5
Frequently asked questions
Short answers to common questions; the numbers link to the sources below.
Common questions
6 answersWhat is casein protein?
Is casein better before bed?
How much casein did studies use?
Casein or whey?
Can casein hurt your kidneys?
In healthy adults, protein above the RDA was consistent with normal kidney function in studies mostly under 6 months. The review excluded kidney disease.9
Is casein safe with a milk allergy?
No. Casein is a milk protein and milk is a major food allergen that supplement labels must declare.12
Sources
12 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.
Sources cited on this page
12 sources- 1Exercise and Athletic Performance: Health Professional Fact SheetFact sheet NIH Office of Dietary Supplements, 2024 · ods.od.nih.gov
- 2Effects of Timing and Types of Protein Supplementation on Improving Muscle Mass, Strength, and Physical Performance in Adults Undergoing Resistance Training: A Network Meta-Analysis.Meta-analysis Int J Sport Nutr Exerc Metab, 2024 · PMID 38039960
- 3Effects of pre-sleep protein consumption on muscle-related outcomes - A systematic review.Systematic review J Sci Med Sport, 2021 · PMID 32811763
- 4Protein Ingestion before Sleep Increases Muscle Mass and Strength Gains during Prolonged Resistance-Type Exercise Training in Healthy Young Men.RCT J Nutr, 2015 · PMID 25926415
- 5Daytime and nighttime casein supplements similarly increase muscle size and strength in response to resistance training earlier in the day: a preliminary investigation.RCT J Int Soc Sports Nutr, 2018 · PMID 29764464
- 6Protein Supplementation after Exercise and before Sleep Does Not Further Augment Muscle Mass and Strength Gains during Resistance Exercise Training in Active Older Men.RCT J Nutr, 2018 · PMID 30247714
- 7Slow and fast dietary proteins differently modulate postprandial protein accretion.PK study Proc Natl Acad Sci U S A, 1997 · PMID 9405716
- 8Casein Protein Processing Strongly Modulates Post-Prandial Plasma Amino Acid Responses In Vivo in Humans.Crossover RCT Nutrients, 2020 · PMID 32751788
- 9A Systematic Review of Renal Health in Healthy Individuals Associated with Protein Intake above the US Recommended Daily Allowance in Randomized Controlled Trials and Observational Studies.Systematic review Adv Nutr, 2018 · PMID 30032227
- 10Comparative Efficacy of Different Protein Supplements on Muscle Mass, Strength, and Physical Indices of Sarcopenia among Community-Dwelling, Hospitalized or Institutionalized Older Adults Undergoing Resistance Training: A Network Meta-Analysis of Randomized Controlled Trials.Meta-analysis Nutrients, 2024 · PMID 38612975
- 11The "on-off" phenomenon in Parkinson's disease. Relation to levodopa absorption and transport.PK study N Engl J Med, 1984 · PMID 6694694
- 12Food Allergies (milk is one of nine major food allergens; allergen source must be declared on packaged foods and dietary supplements)Fact sheet U.S. Food and Drug Administration, 2026 · fda.gov
What changed
Every dated change to this page: what changed, who made it and why.
Change log
2 entries| Date | Change | Who and why |
|---|---|---|
| evidence | Adversarial review: the 2015 pre-sleep trial no longer called casein (its abstract names only a protein supplement, and the fact-sheet attribution could not be opened); 2018 day-vs-night study relabelled a randomized double-blind trial and its funding stated from the full text; 41-man older-adult trial regraded no-effect to D (too small to show no effect); kinetics-trial funding wording matched to the full text. | Writer: Kymata Health EditorialTrigger: adversarial review |
| all | Initial editorial evidence review. Every PMID checked against NCBI E-utilities esummary (title, year, journal) and each cited abstract read; figures taken from the abstracts. Allergen rule from the FDA food allergens page (content dated 2026-03-11). Several cited trials had industry funding or authors with industry ties, as noted in the evidence rows. | Writer: Kymata Health EditorialTrigger: new page |
Supplement & Nutrient Encyclopedia. Educational information only; it is not medical advice and does not replace a clinician. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Statements about supplements have not been evaluated by the FDA.