Should you take collagen supplements? What science says

What science says about collagen in 2024-2025, no bullshit.

Collagen is the supplement everyone talks about and nobody understands. Between the marketing promises ("rebuilds your joints, your skin, your tendons") and the blunt critics ("it is digested like any other protein, it does nothing"), reality is more nuanced, and frankly interesting if you know where to look.

What is collagen, concretely?

Collagen is the most abundant structural protein in your body. It makes up about 70% of the dry weight of your tendons, 60% of your bones, and a good share of your cartilage and skin. There are 28 identified types, but for athletes the most important are:

• Type I: tendons, bones, ligaments, skin. It is the most common type in standard supplements.
• Type II: joint cartilage. This is the one "undenatured" collagen (UC-II) targets.
• Type III: found alongside type I, in skin and blood vessels.

The core problem: your body gets worse at making collagen as you age, especially after 30-35. And some tendons, notably the core of the Achilles tendon, have almost no capacity for renewal in adulthood.

A landmark study (Heinemeier et al., 2013, FASEB J) measured residual radioactivity from atomic bomb tests in human tendons and concluded that the tendon core forms during growth and then barely renews at all. The outer part of the tendon, on the other hand, can adapt. That is where training, and potentially nutrition, play a part.

The big debate: does swallowed collagen become collagen?

That is THE question. The honest answer: not directly, but the mechanism is subtler than that.

When you take a collagen hydrolysate, your digestive enzymes break it down. It does not reach your tendon intact. What reaches your blood are small fragments, called dipeptides and tripeptides (notably Pro-Hyp and Hyp-Gly), which appear in the blood 60 to 120 minutes after ingestion.

This is where it gets interesting: these peptides are more than raw material. They act as signaling molecules that "talk" to fibroblasts (the cells that make tendon collagen) and chondrocytes (the cartilage cells). In vitro, the dipeptide Pro-Hyp stimulates fibroblast proliferation and hyaluronic acid synthesis.

The peptides do not rebuild the tendon directly. They send a signal that amplifies the natural synthesis response triggered by mechanical loading.

The protocol that works (and why vitamin C is essential)

The key study is Shaw, Lee-Barthel, Ross, Wang & Baar (2017), Am J Clin Nutr, run at the University of California Davis with the Australian Institute of Sport. Headline result: 15 g of vitamin C-enriched gelatin, taken 1 hour before loading exercise, doubles the blood markers of collagen synthesis (PINP, an indicator of your fibroblasts' activity).

Serum drawn after this ingestion, applied to lab-engineered ligaments, increased their collagen content and their mechanical properties.

Vitamin C is not a detail. It is a mandatory cofactor of the enzymes that hydroxylate proline, the chemical step that makes collagen stable. Without ascorbate, newly made collagen falls apart. That is the biochemical cause of scurvy. The useful dose in the studies: about 50 mg taken with the collagen.

What the 2024 meta-analysis says (the current reference)

The most complete synthesis available is the meta-analysis by Bischof, Moitzi, Stafilidis & König (2024), Sports Medicine. It pools 19 randomized controlled trials (RCTs) and 768 participants. That is not negligible for this field.

For tendon size, one example: in Jerger et al. (2022), Scand J Med Sci Sports, Achilles tendon cross-sectional area grew by +11.0% in the collagen group against +4.7% in the placebo group over 14 weeks (at 5 g/day). A thicker tendon is generally a sturdier tendon.

By athlete profile: what matters for you

You run (trail, road, marathon)

This is the profile where collagen makes the most sense. Repetitive loading puts heavy stress on tendons and joints. The evidence is there.

Activity-related joint pain is the best-demonstrated outcome. Clark et al. (2008), Curr Med Res Opin: 147 college athletes, 10 g/day of hydrolysate for 24 weeks. Result: a significant reduction in knee, ankle and shoulder pain during running and daily activities. Zdzieblik et al. (2017), Appl Physiol Nutr Metab confirms it with 5 g/day over 12 weeks.

For Achilles tendinopathy: Praet et al. (2019), Nutrients followed 20 runners with Achilles tendinopathy, on 2×2.5 g of specific peptides (30 min before calf strengthening) for 3 months. The functional score (VISA-A) rose by +12.6 points against +5.3 with placebo.

Practical recommendation: 5 to 10 g/day continuously for joint discomfort. If you have a history of tendon problems, 15 g + vitamin C, 30-60 min before your eccentric strengthening sessions.

You cycle

Joint loading is lower than in running, but patellofemoral discomfort (cyclist's knee) is common. 5-10 g/day of hydrolysate can reduce this pain over 12 weeks. If knee osteoarthritis is already present, undenatured collagen UC-II (40 mg/day) has a different mechanism and interesting evidence on osteoarthritis (McAlindon et al., 2016, Nutrition Journal).

Since cycling does not load tendons through impact, add strength training to your program to trigger the collagen synthesis response.

You swim

Low joint stress, tendon risk limited to the upper limbs (shoulder). Collagen is the lowest priority for this profile. If your shoulder is a recurring problem, a targeted protocol makes sense. Otherwise, focus on your overall protein intake.

You lift

Let's be direct: collagen will not build more muscle than whey. It is an incomplete protein. It contains no tryptophan and very little leucine (~0.9 g per 15 g of collagen, against ~4.9 g for whey). Leucine is the amino acid that triggers muscle protein synthesis through the mTOR pathway.

The strongest study on this point: Aussieker, van Loon et al. (2023), Med Sci Sports Exerc, on 45 recreational athletes, with precise isotope tracing (the gold-standard method). Result: after a strength session, whey significantly increases myofibrillar synthesis (actual muscle), collagen does not.

What collagen can do for you in the gym: protect your tendons and adapt them to increasing loads. With heavy loads, tendons take enormous stress. 15 g of hydrolysate + vitamin C before a heavy session (squat, deadlift, leg press) as tendon injury prevention is a rational use.

An emerging trick: take 25 g of whey + 5 g of collagen together. This keeps plasma glycine up (it drops after exercise) while providing the leucine from the whey (Aussieker et al., 2024, IJSNEM).

You are 40+ (or training as you age)

This is the profile with the most favorable benefit/risk ratio. Collagen synthesis declines with age, and tendon adaptation capacity drops. Studies on older subjects (sarcopenic 72-year-old men in Zdzieblik et al., 2015, Br J Nutr) show clearer gains in lean mass and strength than expected, probably through adaptation of connective tissue, which is the limiting factor at that age.

For bones, the signal is solid. König et al. (2018), Nutrients followed 131 postmenopausal women on 5 g/day of specific collagen peptides against placebo for 12 months.

You are a female athlete (especially peri/post-menopause)

The drop in estrogen at menopause speeds up the loss of skin and bone collagen. This is the population with the strongest evidence on bones (König 2018 above) and on body composition (Jendricke et al., 2019, Nutrients: 77 premenopausal women, 15 g/day + strength training, lean mass and strength gains above placebo).

Always combine collagen + resistance training + calcium/vitamin D. None of the three replaces the others.

You are vegetarian or vegan

Let's be honest: "vegan collagen" does not exist in the strict sense. Plants do not make collagen. What goes by that name are "boosters" (vitamin C, hyaluronic acid, silicon, glycine, zinc) that supply the cofactors and precursors of your own synthesis, but not the bioactive peptides themselves (Pro-Hyp, Hyp-Gly). Their effect is indirect and less documented.

There is collagen produced by fermentation with genetically modified Pichia pastoris yeast (Myllyharju et al., 2001, PubMed), technically vegan, with a structure identical to human collagen. But industrial yields remain limited and data on oral efficacy in athletes are almost nonexistent. It will probably be the solution of the future. Today, it is not commercially available at scale.

A rational strategy if you are vegan: maximize vitamin C, glycine (rich foods or the isolated amino acid), zinc, copper, and above all bet on progressive mechanical loading.

If you are pescatarian, marine (fish) collagen is a valid option. Its peptides have a slightly lower molecular weight, but once hydrolyzed, their bioavailability is comparable to bovine collagen.

Which form to choose?

Collagen hydrolysate (powder): the most studied and most bioavailable form. Pick a product whose peptides are under 3,000 Da (good-quality products state it). Powder is the only practical form to reach 15 g.

Food-grade gelatin: valid according to Baar, cheaper, but a higher molecular weight and therefore slightly lower absorption.

Capsules: convenient, but there is no way to reach 5-15 g without swallowing some twenty capsules. Suited only to UC-II (40 mg, immunological mechanism, milligram doses).

Marine vs bovine collagen: marine has a "premium" image, but at the same degree of hydrolysis the two are equivalent for tendons and bones. Marine is rich in type I and suits pescatarians. Bovine (type I and III) is the most used in RCTs.

What science does not tell us yet

The limits are important to know:

• No data on actual injury rates. Every study measures intermediate markers (PINP, tendon size on ultrasound, pain score), not the number of ruptures or injuries avoided.
• Small samples. Several pivotal studies have fewer than 20-30 people.
• Industry funding dominates. Most positive RCTs are funded by GELITA or by teams linked to GELITA.
• No strong institutional position. The ISSN, the ACSM and the IOC have no specific recommendation on collagen for athletes (unlike creatine or protein).

Verdict: for whom, for what, how much?

Collagen is a niche tool, neither a scam nor a revolution.

The non-negotiable condition in every case: mechanical loading. Without exercise, collagen has no reason to end up in your tendons. It amplifies a signal that has to exist first.

This article presents the current scientific data. For a personalized program, consult a healthcare professional.