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

How much of the body is collagen? The number most often repeated is 30 percent of total protein. A group at ETH Zurich decided to measure it, hydrolysing whole mice down to free amino acids and counting the collagen. The answer was about 12 percent in females and 17 percent in males. The authors traced the familiar 30 percent to a 1961 review citing a 1958 measurement of 17.7 percent of total nitrogen, rounded upwards somewhere along the way.

It is a good place to start, because much of what is said about collagen becomes clearer once the biology is on the table. This article explains what collagen is, what it is made of, where the body puts it, why it declines, what vitamin C has to do with it and what happens to collagen you eat. Along the way we explain how we reasoned when we chose the collagen in Beauty Complete. We have written separately about the specific raw material, about the collagen types and their sources and about how much collagen per day the studies used.

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 percent 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.

• New collagen synthesis in skin falls by about 1 percent a year through adult life. Protecting what is already there matters as much as making more, and the pathway that makes more runs through protein and vitamin C.

• Beauty Complete contains six named ingredients: Cartidyss® fish cartilage collagen 500 mg, Hyabest® hyaluronic acid 120 mg, Ceramosides™ phytoceramides 30 mg, vitamin C 60 mg as PureWay-C, vitamin B2 1.4 mg and biotin 50 µg. The 500 mg of collagen is the daily dose used in the raw material's own placebo-controlled study of 46 women over 90 days.

Health Royals Beauty Complete, supplement with Cartidyss marine collagen, Hyabest hyaluronic acid, Ceramosides phytoceramides, vitamin C as PureWay-C, vitamin B2 and biotin

Collagen at Health Royals

Beauty Complete is our daily supplement for the skin, built around six named ingredients: Cartidyss® hydrolysed fish cartilage collagen 500 mg, Hyabest® hyaluronic acid 120 mg, Ceramosides™ phytoceramides 30 mg, vitamin C 60 mg as PureWay-C, vitamin B2 1.4 mg and biotin 50 µg. Each raw material is named, each dose is printed on the label, and the reasoning behind the collagen dose is explained below. Vitamin C contributes to normal collagen formation for the normal function of skin. Biotin contributes to the maintenance of normal skin.

See Beauty Complete, marine collagen and hyaluronic acid

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 they 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 and osteoblasts in bone. Type II is the collagen of cartilage, and we come back to it below.

Plants make none of it. Collagen is an animal protein, so a product sold as vegan collagen is a mixture of amino acids and cofactors meant to support your own synthesis, which is a different proposition from the protein itself.

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 the 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 contains very little.

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 describe it in our article 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. When the body makes less of it and the fibres already in place accumulate wear, 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 adds a slow chemistry of its own: sugars react with collagen that stays in place for fifteen years, producing advanced glycation end products.

There is no blood test for collagen status and, outside genetic disorders and scurvy, no threshold below which a person is low in collagen; the decline is universal, gradual and normal. What we do know is where the pathway can be supported: with enough protein, with vitamin C, and by protecting the collagen already in place from the sun. A supplement for the skin is therefore judged on what it contains and what has been measured, not on the word collagen alone.

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 where the EU's authorised wording on the subject sits. Under Commission Regulation (EU) No 432/2012 it reads "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. Beauty Complete carries 60 mg of vitamin C as PureWay-C, a nutritional dose that sits alongside a normal diet, and that is why the sentence is on our label. The claim belongs to the vitamin and the collagen your own body builds.

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 interesting question is narrower. Do particular small peptides survive digestion intact, reach the circulation and do something there? For the first two steps there is 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, in 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 reach the blood. The most cited paper on the next step, 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.

What we do know is that the useful evidence sits one level down, in trials on a specific raw material where the skin itself was measured. That is where Health Royals starts. When we chose the collagen for Beauty Complete, we began with a named material, its manufacturer and its human study, not with a mechanism. The material is Cartidyss®, a hydrolysed fish cartilage collagen of type II made by Abyss Ingredients in Brittany, a specialist manufacturer of marine raw materials with traceable sourcing. Health Royals works with specialist manufacturers, researchers and supplier networks when raw materials are selected, and this is the kind of manufacturer we look for.

Cartidyss® was studied at 500 mg per day. Beauty Complete contains 500 mg per daily dose. For us, the ingredient cannot be separated from its source, manufacturer and studied dose.

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 is a pleasant food and an uneven 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. What a supplement can add is a defined raw material at a defined daily dose, every day.

What have the trials on collagen and skin measured?

Two things: that the peptides reach the blood, and what happened to the skin of the people who took them.

The absorption is in the section above. On skin, a 2025 systematic review and meta-analysis in the Indian Journal of Dermatology, Venereology and Leprology pooled 10 randomised trials and 646 participants, reporting a standardised mean difference of 1.25 for hydration and 0.61 for elasticity.

Pooling of that kind treats every collagen preparation as the same thing, while the materials tested differ in tissue, type, molecular weight and dose. A higher number is not automatically a better or more evidence-based dose. What matters is the specific raw material and the dose that was actually studied. We explain why the gram figures and the milligram figures in this category cannot be compared in how much collagen per day.

That is why the trial on the individual raw material is more useful than the trial on the category. Cartidyss®, the hydrolysed fish cartilage in Beauty Complete, was tested in a 2021 double-blind, placebo-controlled study in Molecules on 46 women aged 45 to 59, of whom 43 completed, at 500 mg daily for 90 days. The study reported reduced wrinkle measurements around the eyes and nose and increased thickness of the dermis, measured by imaging. A named raw material can be looked up, compared and discussed.

The same reasoning runs through the rest of Beauty Complete. Hyabest® hyaluronic acid, 120 mg, is bio-fermented by Kewpie in Japan to a defined molecular weight, at the daily dose used in its human studies. Ceramosides™ phytoceramides, 30 mg, are a plant lipid extract from Seppic in France, also at the daily dose used in its human studies. Vitamin C 60 mg as PureWay-C, vitamin B2 1.4 mg and biotin 50 µg are nutrients and sit at a nutritional level. Ninety days in the collagen study also means taking the product every day for three months, which is why the jar is designed to stand out on a shelf and become part of the routine rather than disappear into a cupboard.

What does this mean in practice?

Three things follow from the biology.

  • 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 part of the pathway, and it is also the part of the subject where the EU has an authorised wording. The Nordic reference intakes are reachable from food, and Beauty Complete adds 60 mg at a nutritional level.
  • The collagen already in your skin will be there for roughly fifteen years. Protecting what exists, with sun protection above all, 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 supplement for the skin, Beauty Complete, marine collagen and hyaluronic acid, carries Cartidyss® at the 500 mg its study used, with every raw material and dose on the label. We have done the selection so that you do not have to.

Further reading

Frequently asked questions

Do collagen supplements work?
The useful question is which collagen, and at what dose. A named raw material with its own human study can be judged on what that study measured. Cartidyss® was tested on 46 women aged 45 to 59 at 500 mg daily for 90 days, with reduced wrinkle measurements and increased dermal thickness reported, and Beauty Complete carries the same 500 mg per daily dose.

How much collagen do you need to eat a day?
There is no dietary requirement. 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. The studied doses differ by preparation, which we explain in how much collagen per day.

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 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.

Is there such a thing as vegan collagen?
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 the protein itself.

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 authorised wording in 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 percent 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