Collagen peptides: what the studies measured, and what they did not.

Collagen is the main structural protein in skin, tendons and bone. Collagen supplements are made by breaking that protein into short pieces (peptides) so they dissolve in water. The question is what happens after you swallow them.

What the trials measured

Most controlled trials have looked at skin. A 2021 meta-analysis of 19 randomized trials, involving about 1,100 people, found that hydrolyzed collagen taken for 8 to 12 weeks improved measures of skin hydration and elasticity compared with placebo. Doses in those trials ranged from about 2.5 to 10 g a day. Two caveats: many trials were funded by collagen makers, and the products, doses and measurements varied a lot.

Trials on joints are smaller and more mixed. Some found less activity-related joint discomfort; others found little difference.

What collagen is not

Collagen is not a complete protein. It contains no tryptophan and little leucine, the amino acid most linked to muscle building. If your goal is to eat more protein, count collagen as a small extra on top of complete proteins, not instead of them.

Types, sources and labels

• Type I dominates in skin and bone; marine collagen is mostly type I. Once collagen is broken into peptides, the type matters less than the dose.
• Marine collagen comes from fish skin and scales, so it is unsuitable for people with fish allergies. Bovine collagen comes from cattle hides.
• Look for the amount of collagen per serving, a heavy-metals result (especially for marine collagen), and no added sugar.

The honest summary

If you want to try collagen for skin, the evidence supports 8 to 12 weeks at a dose like the trials used. Keep expectations modest, and keep sunscreen, sleep and protein in your diet doing most of the work.

Sources

• de Miranda RB et al., Effects of hydrolyzed collagen supplementation on skin aging: a systematic review and meta-analysis, International Journal of Dermatology, 2021.
• Paul C et al., Significant amounts of functional collagen peptides can be incorporated in the diet while maintaining indispensable amino acid balance, Nutrients, 2019.

This guide is general information, not medical advice. Talk to your doctor or pharmacist before starting a supplement if you are pregnant or nursing, take medication, or have a medical condition.