Collagen supplement: does it really work for skin, tendons and bone?

A collagen supplement is protein from animal connective tissue, cut into short peptides so you absorb it. For skin, randomized studies fairly consistently show improvements in hydration and elasticity. For tendons, joints and bone the evidence is considerably thinner.

And there is a detail that almost never makes it onto the tub.

Collagen is an incomplete protein. It contains virtually no tryptophan and little of the amino acids your muscles respond to, so counting those 10 grams toward your daily protein intake flatters your numbers.

What is collagen and what does a supplement do?

Collagen is the most abundant protein in your body and forms the structure of skin, tendons, ligaments, cartilage and bone. You make it yourself, and that production gradually declines from around age thirty.

A supplement does not deliver it straight to your skin.

What you swallow is broken down in your gut into amino acids and small peptides. The working hypothesis is that some of those peptides reach your bloodstream and prompt your own connective tissue cells to build more. That is plausible, but it is a hypothesis and not an established mechanism.

Does collagen work for your skin?

This is the claim with the best support. Several placebo-controlled studies using 2.5 to 10 grams of collagen peptides daily over 8 to 12 weeks reported improvements in skin hydration and elasticity.

The effects are measurable but modest.

There is an important caveat. A large share of this research is funded by collagen powder manufacturers, groups are often small and study duration is short. That does not invalidate the results, but it does make them less convincing than the sheer number of studies suggests.

Does collagen work for your joints and tendons?

Here it gets thinner. Some studies report fewer joint complaints in people taking collagen, often combined with vitamins and other compounds, which leaves you unable to tell which ingredient did it.

For tendon recovery in athletes the evidence is currently too thin to promise anything.

What does reliably move bone density sits in bone density in athletes.

What are the side effects of collagen?

Collagen peptides are generally well tolerated in studies. What gets reported is usually mild: a full feeling, some burping, occasionally an unpleasant aftertaste.

The points to watch sit elsewhere.

Most powders come from cattle, pig or fish, so with a fish allergy the source matters. If you stack several supplements, the chance of unwanted overlap is greater than with collagen alone, especially when vitamins have been added.

If you take medication or are pregnant, check with your doctor or pharmacist before adding anything new.

Is collagen also in food?

Yes, in anything containing connective tissue: bone broth, chicken with skin, brawn, and to a lesser extent tougher cuts of meat. A good broth supplies a few grams.

Your body also makes it, provided the building blocks are there.

For that you need enough protein and vitamin C, which acts as a cofactor in production. The Dutch nutrition centre Voedingscentrum uses roughly 0.8 grams of protein per kilo of body weight per day as a baseline for adults, and for strength athletes practice runs higher.

A shortage of building blocks is rare in the Netherlands. Anyone eating normally is not missing them.

Which blood values are relevant here?

There is no blood value that measures your collagen status. What you can follow are the things that hold back connective tissue repair when they are off.

Think of your vitamin D, your iron stores and your hs-CRP as a measure of low-grade inflammation.

That last one is the most useful. If your recovery lags while you are doing everything right, a raised inflammatory value says more than any powder, and we work that line out in chronic low-grade inflammation.

Where do you start?

If you want to try it for your skin, take 10 grams a day and give it 12 weeks, because anything shorter tells you nothing. Do not count those 10 grams toward your protein target.

Expect a small effect or no effect.

Our vitamin D test shows whether the building block you can actually influence is in order, with an assessment by a BIG-registered doctor. For the rest of your cupboard, 9 supplements for athletes is the honest walkthrough, and the broader approach sits in healthy ageing as an athlete.

References

1. Bolke L, Schlippe G, Gerß J, Voss W. A collagen supplement improves skin hydration, elasticity, roughness, and density: results of a randomized, placebo-controlled, blind study. Nutrients. 2019. PMID 31627309.
2. Proksch E, Segger D, Degwert J, et al. Oral supplementation of specific collagen peptides has beneficial effects on human skin physiology: a double-blind, placebo-controlled study. Skin Pharmacology and Physiology. 2014. PMID 23949208.
3. Kim DU, Chung HC, Choi J, et al. Oral intake of low-molecular-weight collagen peptide improves hydration, elasticity, and wrinkling in human skin: a randomized, double-blind, placebo-controlled study. Nutrients. 2018. PMID 29949889.
4. Czajka A, Kania EM, Genovese L, et al. Daily oral supplementation with collagen peptides combined with vitamins and other bioactive compounds improves skin elasticity and has a beneficial effect on joint and general wellbeing. Nutrition Research. 2018. PMID 30122200.
5. Voedingscentrum (Netherlands Nutrition Centre). Protein. Accessed 2026.

Disclaimer

Every blood test result includes a professional assessment by a BIG-registered doctor. This article provides general information and is not a substitute for medical advice. Discuss your results with your doctor before making treatment decisions.