Collagen

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By Nikola · Precision Nutrition L1 · Updated 5 November 2026

Collagen is the most abundant protein in the body, a main building block of skin, bone, tendons, cartilage and other connective tissue, and supplements sell it as hydrolysed collagen or collagen peptides for skin and joints. Your body makes it from amino acids such as glycine, proline and hydroxyproline, with help from vitamin C and zinc. Swallowed collagen is digested into amino acids. The evidence for skin and joints is thin: most trials are funded by the industry, and a 2025 meta-analysis found no effect on skin in independently funded or high-quality trials. Collagen is also an incomplete protein, since it lacks the essential amino acid tryptophan.

What the research says

• Skin – weak evidence. A 2025 meta-analysis in The American Journal of Medicine pooled 23 randomised trials with 1,474 people. Taken together, they showed better skin hydration, elasticity and fewer wrinkles. But trials without industry funding showed no effect on any of these, while industry-funded trials did, and high-quality trials showed no significant effect at all. The authors concluded: “There is currently no clinical evidence to support the use of collagen supplements to prevent or treat skin aging.” Industry groups disputed how funding and quality were classified, so the debate is not closed.
• Osteoarthritis – weak to moderate evidence. A 2019 meta-analysis of placebo-controlled trials found that collagen lowered the total WOMAC score, a standard osteoarthritis questionnaire, by 8 points and improved stiffness and the visual analogue scale (VAS) score. The WOMAC pain and function sub-scores did not change significantly. A 2020 review of 41 studies found that all reported benefits regardless of their quality, that more than a third came from Asia, and called for longer, larger placebo-controlled trials.
• Joint pain in active people – weak evidence. A 2021 systematic review of 15 randomised trials, 12 of them in recreational athletes, found the clearest benefits for joint function and pain. Collagen synthesis rose with 15 g a day.
• Muscle – no advantage. In the same review, collagen did not raise muscle protein synthesis more than the same amount of higher-quality protein. For muscle, whey protein or ordinary food protein does the job better.
• Who pays for the research. Harvard’s Nutrition Source notes that “most if not all” collagen supplement research is funded or partly funded by related industries.
• What the EU allows. Regulation (EU) 432/2012 has no authorised claim for collagen. The claims about collagen belong to vitamin C: “Vitamin C contributes to normal collagen formation for the normal function of” blood vessels, bones, cartilage, gums, skin and teeth, for foods that are at least a source of vitamin C.

Dose and forms

• Hydrolysed collagen or collagen peptides. Collagen broken into smaller pieces, the form most supplements use. It was the form tested in 28 of the 41 studies in the 2020 review.
• Undenatured collagen. Sold as a separate form; it was studied in 9 of those 41 studies.
• Gelatin. A form of collagen made by boiling animal bones, cartilage and skin for several hours (Harvard).
• Dose and time. 15 g a day raised collagen synthesis in active people (2021 review). In osteoarthritis studies, treatment usually lasted 3-6 months. There is no official recommended intake for collagen.
• Vitamin C. Your body needs vitamin C to make collagen (NIH ODS); in scurvy, the lack of vitamin C impairs collagen synthesis and weakens connective tissue.

Food sources

In food, collagen comes only from animal tissue with connective tissue, such as meat and fish, including the skin and bones of fish like salmon or sardines (Harvard). Gelatin and stock made from bones are the most direct sources. USDA does not list collagen as a nutrient, so the table shows total protein and, for gelatin, the amino acids that make collagen different.

Food	Protein, 100 g	Portion	Protein per portion
Gelatin, dry powder, unsweetened	85.6 g	1 envelope, 7 g	6.0 g
Chicken stock, home-prepared	2.52 g	1 cup, 240 g	6.0 g
Beef stock, home-prepared	1.97 g	1 cup, 240 g	4.7 g

Per 100 g	Glycine	Proline	Leucine	Tryptophan
Gelatin, dry	19.0 g	12.3 g	2.45 g	0 g
Egg, whole, raw	0.43 g	0.51 g	1.09 g	0.17 g

Source: USDA FoodData Central, SR Legacy, checked 5 November 2026: gelatin FDC 169599, chicken stock FDC 172884, beef stock FDC 172883, egg FDC 171287. Portions are USDA household measures; values per portion are calculated and rounded.

The second table is the “incomplete protein” point in numbers: gelatin is mostly glycine and proline and has no tryptophan, so it cannot be your main protein, while eggs do provide tryptophan. For vitamin C, NIH ODS lists citrus such as oranges, red and green peppers, kiwi, broccoli, strawberries, baked potatoes and tomatoes.

Side effects and interactions

• Few reported side effects. Harvard notes that research so far has not shown negative side effects in people taking collagen supplements.
• No pre-market checks. In the US, the FDA does not review supplements for safety or effectiveness before they are sold (Harvard).
• Heavy metals in bone broth. One study cited by Harvard found that broth made from chicken bones had three times the lead of broth made from the meat only. It is a single study, but worth knowing.
• Medicines. On regular medication, ask your pharmacist first.

Who should avoid it

• Vegetarians and vegans. Collagen and gelatin come from animals; there is no plant collagen in food.
• People with fish allergy. Collagen also occurs in fish skin and bones (Harvard), so check the source on the label.
• People with chronic kidney disease. Collagen is protein and counts toward your daily total. Some people with CKD need a moderate protein intake (NIDDK), so agree the amount with your doctor or dietitian.
• Anyone relying on it as main protein. Because it lacks tryptophan, it cannot replace complete protein foods.

How to choose a good product

• Type and source. The label should say hydrolysed collagen, collagen peptides, gelatin or undenatured collagen, and from which animal or fish.
• Grams per serving. Check the amount per serving against the doses used in studies, such as 15 g a day.
• No hidden blends. Avoid proprietary blends that do not list amounts (NIH ODS).
• Independent testing. Seals from programmes such as NSF Certified for Sport, Informed-Choice or BSCG show that a product was tested for banned substances (NIH ODS).

FAQ

Does collagen really work for skin?

The evidence is weak. A 2025 meta-analysis of 23 trials found benefits for hydration, elasticity and wrinkles only in industry-funded and lower-quality trials; independent and high-quality trials showed no effect. The authors concluded there is no clinical evidence that collagen prevents or treats skin ageing.

Is collagen a complete protein?

No. Gelatin, a form of collagen, has 0 g of tryptophan per 100 g in USDA data, and tryptophan is an essential amino acid. Collagen counts toward your protein intake but cannot be your only protein source.

Should I take vitamin C with collagen?

Your body needs vitamin C to make its own collagen, and the EU allows claims that vitamin C contributes to normal collagen formation. We found no verified evidence that taking the two together improves results. Your own collagen production depends on enough vitamin C, which peppers, kiwi, citrus and broccoli provide.

Related entries and articles

• Vitamin C and zinc – the nutrients your body needs to make collagen
• Whey protein and creatine
• Bell peppers, kiwi and broccoli
• Eggs
• Zinc-rich foods: best sources and how much you need
• Stuffed peppers with bulgur and feta

Sources

1. Myung SK, Park Y (2025). Effects of Collagen Supplements on Skin Aging: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. The American Journal of Medicine 138(9):1264-1277. doi:10.1016/j.amjmed.2025.04.034. europepmc (ebi.ac.uk)
2. NutraIngredients (26 August 2025): Industry pushes back on meta-analysis concluding collagen supplements show no benefit for skin aging. nutraingredients.com
3. García-Coronado JM, et al. (2019). Effect of collagen supplementation on osteoarthritis symptoms: a meta-analysis of randomized placebo-controlled trials. International Orthopaedics 43(3):531-538; Honvo G, et al. (2020). Role of Collagen Derivatives in Osteoarthritis and Cartilage Repair: A Systematic Scoping Review With Evidence Mapping. Rheumatology and Therapy 7(4):703-740. Khatri M, et al. (2021). The effects of collagen peptide supplementation on body composition, collagen synthesis, and recovery from joint injury and exercise: a systematic review. Amino Acids 53(10):1493-1506. doi:10.1007/s00726-021-03072-x. europepmc (ebi.ac.uk)
4. Harvard T.H. Chan School of Public Health, The Nutrition Source: Collagen. nutritionsource.hsph.harvard.edu
5. USDA FoodData Central, SR Legacy: Gelatins, dry powder, unsweetened (FDC 169599); Soup, stock, chicken, home-prepared (FDC 172884); Soup, stock, beef, home-prepared (FDC 172883); Egg, whole, raw, fresh (FDC 171287). fdc.nal.usda.gov
6. NIH Office of Dietary Supplements: Vitamin C, Fact Sheets for Health Professionals and for Consumers. ods.od.nih.gov
7. Commission Regulation (EU) No 432/2012 – permitted health claims (vitamin C and collagen formation). legislation.gov.uk
8. NIH Office of Dietary Supplements: Dietary Supplements for Exercise and Athletic Performance, Fact Sheet for Consumers. ods.od.nih.gov
9. NIDDK: Healthy Eating for Adults with Chronic Kidney Disease. niddk.nih.gov

This page is for information only and is not medical or dietary advice.