Casein
A slow milk protein; no proven edge over other proteins at night
What it is
The main protein in milk: it makes up 80% of dairy protein. It is digested more slowly than whey, so amino acids reach the blood more slowly.
Benefits
Like any protein, it helps you reach your daily target. According to ISSN, 30–40 g of casein before sleep raises overnight muscle protein synthesis. AIS notes, however, that research confirming casein beats other proteins at night is lacking. ISSN also suggests fast-digesting whey may be better for muscle adaptation.
Dose
Before sleep: 30–40 g (ISSN); studies cited by NIH ODS used 27.5 or 40 g. The general protein guidance still applies: 20–40 g or 0.25 g/kg per serving (ISSN), no more than 40 g at once (AIS).
When to take it
Most often before sleep: in studies casein was taken 30 minutes before bed. But a study where it was taken either in the morning or in the evening found no difference in body composition or performance between the groups (ISSN).
Who it's for
People who fall short on protein from food and find it handy to top up in the evening: in people doing resistance training, protein before sleep can raise overnight protein synthesis (NIH ODS). The sources give no specific guidance on who needs casein in particular.
Who can skip it
If food covers your protein, you don't need it: most athletes reach their targets without supplements (AIS). There is no reason to swap another protein for casein just for the night: its special value at bedtime is unconfirmed (AIS).
Forms
Casein, calcium caseinate and casein hydrolysate are sold (AIS). Casein clots in the acidic environment of the stomach, so it is digested slowly. Hydrolysate is absorbed faster: in a study of 10 elderly men its amino acids appeared in the blood 27% faster than from intact casein, but the difference in muscle protein synthesis did not reach significance. In another study in older men whey protein stimulated synthesis more than both casein and its hydrolysate. We found no comparisons of micellar casein with caseinates for training outcomes.
Safety
The sources have no separate safety data for casein. For protein in general: in healthy active people higher intake has shown no harm to the liver or kidneys (ISSN); in kidney failure protein is restricted. Milk is an allergen some people need to avoid (AIS). We found no data for pregnancy or teenagers: see a doctor first.
From regular food
Work out your numbers
This is a summary of public sources, not medical advice. If you have a health condition, are pregnant or take medication, talk to a doctor before taking a supplement.
Sources
- International Society of Sports Nutrition Position Stand: protein and exercise . ISSN, 2017.
- AIS Sports Supplement Framework — Isolated Protein Supplements, Practitioner Fact Sheet . AIS, 2025.
- Dietary Supplements for Exercise and Athletic Performance — Health Professional Fact Sheet . NIH ODS, 2024.
- Ingestion of a protein hydrolysate is accompanied by an accelerated in vivo digestion and absorption rate when compared with its intact protein . American Journal of Clinical Nutrition, 2009.
- Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men . American Journal of Clinical Nutrition, 2011.
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