COLLAGEN FOR TENDONS AFTER 50: WHAT THE EVIDENCE SUPPORTS, AND WHERE IT STOPS

Collagen is the one supplement that seems to have escaped the usual skepticism. The tendon evidence is better than most supplement evidence — and it is also narrower than almost anyone selling it admits.

Why Tendons Are the Right Question After 50

Muscle responds to training quickly. Tendon does not. Tendon and ligament tissue is poorly vascularized, turns over slowly, and adapts on a longer timeline than the muscle pulling on it. That mismatch is why so many masters athletes get hurt in the third month of a new program rather than the first: the engine upgraded faster than the cables connecting it.

So the question is a fair one. If you can nudge collagen synthesis in the tissue that limits you, that is worth knowing about. Here is what has actually been measured.

The Study Everyone Cites

The foundational work is Shaw and colleagues, published in The American Journal of Clinical Nutrition in 2017. Eight healthy men completed a randomized, double-blinded crossover protocol, taking either 5 or 15 grams of vitamin C–enriched gelatin, or a placebo, one hour before six minutes of rope skipping — repeated three times a day, with at least six hours between bouts, for three days.

Supplementation raised circulating glycine, proline, hydroxyproline, and hydroxylysine — the amino acid building blocks of collagen — peaking about an hour after the dose. That is the origin of the "take it an hour before you load the tissue" advice, and the timing is genuinely grounded.

But read the second half carefully, because this is where the popular retelling goes wrong. The improvement in collagen content and mechanical strength was measured in engineered ligament constructs grown in a lab and bathed in the participants' blood serum — not in the tendons of the eight men themselves. That is a real and interesting result. It is not the same as demonstrating stronger human tendons, and the sample was eight people.

The mechanism is credible. The leap from "serum that behaves differently in a dish" to "your Achilles is more durable" is a leap, not a finding.

What the Pooled Evidence Says Now

A 2025 systematic review published in the Journal of Functional Morphology and Kinesiology gathered eight randomized controlled trials covering 257 participants. Its conclusions are unusually specific, and they cut both directions:

• Tendon cross-sectional area and tendon stiffness increased — rated GRADE A, the review's strongest evidence tier, when 15–30 g of collagen with at least 50 mg of vitamin C was paired with high-intensity resistance training at 70 percent of one-rep max or above.
• Muscle strength did not improve — also rated GRADE A, but as strong evidence against an effect. Collagen is not a strength supplement.
• Muscle cross-sectional area and physical performance were conflicting — GRADE C. Unsettled.

Note what the training requirement implies. In every one of these protocols, collagen was an add-on to hard loading. Nothing here suggests the supplement does anything on its own. The loading is the intervention; the collagen is, at best, a modifier.

The Part That Applies Least to Us

Here is the caveat that matters most for this audience, and the one you will rarely see mentioned: the participants in that 2025 review were aged 18 to 52, and predominantly male.

The tendon evidence is drawn overwhelmingly from young men. I could not find a trial that measured tendon structural outcomes specifically in athletes over 60. That is not the same as saying collagen fails in older athletes — it is saying the direct evidence has not been collected, and the population most interested in tendon durability is the population least represented in the data.

The closest older-adult trial addresses muscle, not tendon. Zdzieblik and colleagues, in the British Journal of Nutrition in 2015, randomized 53 men with sarcopenia — mean age 72 — to 15 g/day of collagen peptides or placebo alongside 12 weeks of supervised resistance training three times a week. The collagen group gained more fat-free mass, lost more fat mass, and improved strength more than placebo. Worth knowing, and worth weighing against the fact that the study was funded by a collagen manufacturer and a 2025 corrigendum disclosed that a co-author is named as co-inventor on a related patent application. The corrigendum corrected the disclosures, not the results — but industry-funded supplement trials warrant a heavier thumb on the scale of skepticism.

Pain and Injury: Thinner Than Advertised

Collagen is widely marketed for joint pain, and the trial evidence there is smaller and less consistent than the tendon-structure evidence. A 2025 randomized, double-blind, placebo-controlled trial in BMC Musculoskeletal Disorders gave 32 patients with meniscopathy a mixed type I, II, and III collagen product for eight weeks. Pain, quality of life, kinesiophobia, and foot function scores improved significantly. Leg strength was borderline at p=0.057. Back strength, proprioception, and balance showed no significant improvement at all.

Thirty-two people over eight weeks is a pilot, not a verdict. Take the direction as a hint and the magnitude with caution.

The Protocol

If you want to test this on yourself, the evidence supports a fairly narrow version of the practice:

• 15 g of collagen peptides or gelatin, with at least 50 mg of vitamin C. That is the dose range the tendon trials actually used. Higher intakes have been studied up to 30 g; there is no evidence that going beyond the studied range buys anything.
• Take it roughly 60 minutes before loading the tissue. This follows directly from the amino acid peak in the Shaw data — it is the best-supported detail in the entire protocol.
• The loading is non-negotiable. Every positive trial paired supplementation with hard resistance training. Collagen taken on the couch has no evidence behind it.
• Give it 12 weeks minimum. The trials ran three months or longer. Tendon does not remodel on a two-week timeline.
• Keep total protein high regardless. Collagen is an incomplete protein and a poor source of leucine. It belongs on top of adequate total protein intake, never in place of it.
• Expect tendon adaptation, not strength. The strongest evidence in the entire literature is that this will not make you stronger. If the label promises that, the label is ahead of the data.

This is a modest, well-bounded intervention with a plausible mechanism and a real but narrow evidence base that was largely built on men half our age. That is an honest reason to try it. It is not a reason to expect much.

For educational purposes only. Not medical advice. Consult your physician before making changes to your health regimen.