What is collagen good for, and what happens when it declines

What is collagen good for, and what happens when it declines

A group at ETH Zurich recently did something nobody had bothered to do properly. They hydrolysed whole mice down to free amino acids and measured how much of the total protein was actually collagen. The answer was about 12 percent in females and 17 percent in males. The figure repeated in more than fifty published papers, and in almost every article ever written about collagen supplements, is 30 percent. The authors traced it to a 1961 review citing a 1958 measurement of 17.7 percent of total nitrogen, inflated somewhere along the way.

That is a fitting place to start, because collagen is one of the most discussed and least explained molecules in the supplement aisle. This article is the explainer, and it recommends no type, source or dose. We have written about specific collagen raw materials separately.

The short version

• Collagen is a family of structural proteins built from three chains wound into a triple helix, with glycine in every third position. In skin it accounts for around 70 per cent of the dry mass, and its half-life there is roughly 15 years, which makes it one of the longest-lived materials in the body.

• The nuance that matters most: no collagen health claim is authorised anywhere in the EU. The 2025 meta-analysis of 23 randomised trials and 1474 participants produced a positive pooled result, but in the subgroups without industry funding, and among the higher quality trials, there was no effect on hydration, elasticity or wrinkles.

• Beauty Complete contains Cartidyss, a marine type II collagen complex from fish cartilage, at 500 mg per daily dose, alongside vitamin C as PureWay-C. Vitamin C contributes to normal collagen formation for the normal function of skin. About the collagen itself we say nothing, because there is nothing authorised to say.

Health Royals Beauty Complete, supplement with Cartidyss marine collagen, Hyabest hyaluronic acid, Ceramosides and vitamin C as PureWay-C

Collagen at Health Royals

Beauty Complete contains Cartidyss, a hydrolysed marine type II collagen complex from fish cartilage, at 500 mg per daily dose. That is the dose used in the ingredient's own trial of 46 women over 90 days, in which skin structure was measured by imaging. It also carries hyaluronic acid as Hyabest, phytoceramides as Ceramosides and vitamin C as PureWay-C. Vitamin C contributes to normal collagen formation for the normal function of skin. For collagen there is no authorised claim, and we make none.

See Beauty Complete

What is collagen?

Collagen is a family of fibrous structural proteins that animals use to build the scaffolding between their cells.

It is not a single molecule. Several genetically distinct collagens exist and differ in how they assemble: some form the long striated fibrils found in tendon and skin, others form sheets and networks. Type I is by far the most abundant. Fibroblasts make it in skin, chondrocytes in cartilage, osteoblasts in bone.

Plants make none of it. Collagen is an animal protein, which is why nothing sold as vegan collagen is collagen. Such products are mixtures of amino acids and cofactors meant to support your own synthesis, a different proposition.

What is collagen made of?

Three protein chains wound around each other into a triple helix, with each chain built from one repeating three amino acid pattern.

That pattern is Gly-X-Y. As a 2025 review in Discover Applied Sciences puts it, every chain runs to roughly 1000 amino acid residues of repeating Gly-X-Y triplets, where X is usually proline and Y is usually hydroxyproline. Glycine has to sit in every third position because it is the smallest amino acid there is, a single hydrogen atom for a side chain, and the only one that fits the crowded interior of the helix.

Hydroxyproline is the one worth knowing about. It is not written into the chain during translation but made afterwards, by hydroxylating proline residues already in place, and that extra hydroxyl group is what stabilises the finished triple helix. It occurs almost nowhere else in the body, which is why laboratories use it as the analytical stand-in for collagen, as the mouse study above did.

Once the helices leave the cell they are trimmed, packed side by side into fibrils and cross-linked. The cross-links are what turn a soluble protein into load-bearing material.

What does collagen do in the body?

It carries tensile load. Collagen is the material that lets skin resist tearing, tendon transmit muscle force to bone, and cartilage take compression without wearing through.

The distribution follows the mechanics. In those same whole-animal measurements, collagen made up roughly 40 to 50 percent of total protein in tendon, 25 to 35 percent in bone and 20 to 38 percent in skin, against about 0.1 percent in brain and liver. Tissue that holds something together is largely collagen. Tissue that computes or metabolises is barely collagen at all.

In human skin, collagen accounts for around 70 percent of the dry mass, essentially all of it in the dermis, the living layer under the epidermis. That layer decides how skin behaves mechanically, and we have described it in our piece on the biology of skin.

One property matters more than most people realise: collagen is extremely long-lived. Using the racemisation of aspartic acid as a molecular clock, a 2000 study in the Journal of Biological Chemistry put the half-life of collagen in human skin at about 15 years, and in articular cartilage at about 117 years. Most proteins are replaced within days. Collagen is laid down and then lived in.

What is collagen good for, and what happens when it declines?

Collagen is what gives connective tissue its strength and elasticity, so when the body makes less of it and the fibres already in place accumulate damage, skin, tendon and cartilage gradually lose stiffness and resilience. That is ordinary ageing, not a deficiency and not a disease.

The decline is measurable. A 2022 review in Biogerontology summarises forearm measurements across ages 15 to 93 showing that skin collagen falls close to linearly by about 1 percent a year through adult life, and reports that collagen synthesis in the skin of people over 80 runs some 68 to 75 percent below young skin.

Two processes run at once. Less new collagen is made, and the existing collagen is degraded and chemically altered. The same review notes that the collagen-degrading enzyme MMP-1 is strongly upregulated with age, leaving more fragmented collagen behind, and that cross-links are significantly reduced in photoaged skin. The long half-life makes the chemistry worse: sugars react slowly with collagen that stays in place for fifteen years, producing advanced glycation end products.

Worth being blunt: there is no blood test for collagen status and no threshold below which a person is low in collagen, outside genetic disorders and scurvy. The decline is universal, gradual and normal.

Why does the body need vitamin C to build collagen?

Because the enzymes that hydroxylate proline and lysine in the collagen chain use vitamin C as a cofactor, and without those hydroxylations the helix does not hold together.

A 2017 review in Nutrients states it directly: vitamin C acts as a cofactor for the proline and lysine hydroxylases that stabilise the collagen molecule. Without hydroxyproline the triple helix is unstable at body temperature and the cell degrades the chains instead of exporting them. Scurvy is the extreme version of that failure. Skin holds vitamin C actively, with the epidermis carrying two to five times more than the dermis.

The Nordic Nutrition Recommendations 2023 set the recommended intake at 95 mg a day for adult women and 110 mg for adult men, reachable from food. We have written separately about what vitamin C does beyond collagen.

This is also the only officially authorised statement anywhere near this subject. Under Commission Regulation (EU) No 432/2012, EU law permits the wording "Vitamin C contributes to normal collagen formation for the normal function of skin", usable when a food is at least a source of vitamin C. Parallel wordings exist for bones, cartilage, gums, teeth and blood vessels. Read what the claim attaches to: it is a claim about vitamin C, not about swallowing collagen.

What happens to the collagen you eat?

It is digested. Cooking and stomach acid denature the triple helix, and the chains are cut into free amino acids and short peptides before anything crosses the gut wall. No swallowed collagen arrives in your skin as collagen.

The genuinely open question is narrower. Do particular small peptides survive digestion intact, reach the circulation and do something there? For the first two steps there is real human evidence. In a 2005 study in the Journal of Agricultural and Food Chemistry, volunteers given gelatin hydrolysates from pig skin, chicken feet and cartilage showed peptide-bound hydroxyproline in plasma rising to 20 to 60 nmol per mL, one to two hours after ingestion, with prolyl-hydroxyproline, usually written Pro-Hyp, the dominant form.

A 2024 randomised, double blind crossover trial in Frontiers in Nutrition repeated the experiment with better analytics, though in only six volunteers. A single 10 g dose of hydrolysate from fish skin, pig skin or bovine hide produced peak plasma concentrations 100 to 130 minutes after intake, with 36 to 47 percent of the circulating hydroxyproline in peptide-bound rather than free form. Pro-Hyp was again the most abundant.

So the peptides do reach the blood. Whether they reach the human dermis is the step nobody has shown directly. The most cited paper on the question, from 2017, measured plasma in humans, identifying 17 collagen-derived peptides with Gly-Pro-Hyp particularly enriched, and then measured skin in mice, where Pro-Hyp accumulated. The human half and the skin half are from different species, a distinction that disappears in marketing copy.

Which foods contain collagen?

Animal connective tissue, and the cuts built around it: skin, bone, cartilage, tendon, chicken skin, pork rind, fish skin, oxtail, shank, and gelatin, which is collagen that heat has already denatured.

No plant food contains any. Vegetables contribute the amino acids and the vitamin C that the pathway needs, not the protein itself.

Bone broth is the food most often described as a collagen source, and the one that has actually been measured. A 2019 study in the International Journal of Sport Nutrition and Exercise Metabolism compared broths against the collagen doses used in research and found that broth made to a standardised recipe delivered significantly less hydroxyproline, glycine and proline than a 20 g supplemental dose, with wide variation between recipes and commercial samples. Broth cannot be relied on as a consistent source.

There is no dietary requirement for collagen. Glycine and proline are not essential amino acids and the body can make them. What collagen synthesis needs from food is enough total protein and enough vitamin C.

Why do people take collagen, and what does the research not show?

No collagen health claim is authorised anywhere in the EU, and the most recent meta-analysis of skin trials concluded that the clinical evidence does not support the practice.

The EU Register of nutrition and health claims lists authorised and non-authorised claims with the reasons for refusal. Collagen appears only on the non-authorised side. In 2011, EFSA assessed an application for collagen hydrolysate and maintenance of joints and concluded that a cause and effect relationship had not been established.

On skin, a 2025 meta-analysis in The American Journal of Medicine pooled 23 randomised controlled trials with 1,474 participants. The headline pooled result was positive for hydration, elasticity and wrinkles. The subgroup analysis is the part worth reading: trials that received no industry funding showed no effect on any of the three outcomes, and neither did the higher quality trials. The authors' conclusion was that there is currently no clinical evidence to support the use of collagen supplements to prevent or treat skin ageing.

That is the honest state of the field. Peptides are absorbed, they circulate, and in rodents reach the skin. What has not been shown is a reliable, measurable effect in people once the industry-funded trials are set aside. Anyone telling you otherwise is quoting the headline figure and skipping the subgroups.

What this means in practice

Three things follow from the biology, and none of them require buying anything.

  • Your body builds collagen from ordinary amino acids it can obtain or make itself. Total protein intake does more work here than the source of that protein.
  • Vitamin C is not optional in this pathway. It is also the only element of the whole subject carrying an authorised EU claim, and the Nordic reference intakes are reachable from food.
  • The collagen already in your skin will be there for roughly fifteen years. Protecting what exists is at least as consequential as trying to make more.

For the next layer of detail, our skin page collects the biology and the ingredients in one place. Health Royals' own skin formula, Beauty Complete, lists every raw material and dose on the label.

Further reading

Frequently asked questions

Do collagen supplements work?
The honest answer is that the question is unsettled. The 2025 meta-analysis of 23 randomised trials and 1474 participants produced a positive pooled result for hydration, elasticity and wrinkles, but the trials without industry funding showed no effect on any of those outcomes, and neither did the higher quality trials. The authors concluded that there is currently no clinical evidence to support the practice.

How much collagen do you need to eat a day?
None. Glycine and proline are not essential amino acids and the body can make them, so there is no dietary requirement for collagen. What collagen synthesis needs from food is enough total protein and enough vitamin C.

Can you get collagen from food?
Yes, from connective tissue: skin, bone, cartilage, tendon, pork rind, fish skin, oxtail and gelatin. Bone broth is the source most often named and the one that has actually been measured, and a 2019 study found broth delivered significantly less hydroxyproline, glycine and proline than a 20 g supplemental dose, with wide variation between recipes. Broth cannot be relied on as a consistent source.

Is there such a thing as vegan collagen?
No. Collagen is an animal protein and no plant makes any. What is sold as vegan collagen is a mixture of amino acids and cofactors meant to support your own synthesis, which is a different proposition from what the word on the pack implies.

Why is vitamin C always mentioned alongside collagen?
Because the enzymes that hydroxylate proline and lysine in the collagen chain use vitamin C as a cofactor, and without those hydroxylations the triple helix is unstable at body temperature. It is also the only authorised wording anywhere near the subject: vitamin C contributes to normal collagen formation for the normal function of skin. The Nordic recommendations set 95 mg a day for adult women and 110 mg for adult men, reachable from food.

When does the body's collagen start to decline?
Gradually across adult life. Forearm measurements across ages 15 to 93 show skin collagen falling close to linearly by about 1 per cent a year, while the collagen already in place is degraded and chemically altered. That is ordinary ageing rather than a deficiency, and there is no blood test for collagen status.

Sources