Collagen and vitamin C
Evidence: limited
Biologically plausible and low-risk, with promising mechanistic and early structural data for tendon and bone. Not yet shown to prevent injury or improve performance in runners.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are injured, unwell or weighing up a supplement or a change to your diet, speak to a doctor, physiotherapist or registered dietitian who knows your situation.
Most ergogenic supplements aimed at runners either work on muscle and the energy systems or do not work at all. Collagen with vitamin C is different: the target is the connective tissue, the tendons, ligaments and bone that take the repeated load of running. The evidence is thinner than for the proven aids, but the mechanism is sound and the downside is small, which sets it apart from the supplements that do not hold up.
The rationale
Collagen is the main structural protein of tendon, ligament and bone, and it is unusually rich in the amino acids glycine, proline and hydroxyproline. Building it requires vitamin C as a cofactor: the enzymes that hydroxylate proline and lysine, the step that lets collagen form its stable triple helix, depend on it. The idea behind timed gelatin or collagen dosing is to flood the blood with these amino-acid precursors, plus their vitamin-C cofactor, in the short window when exercise has raised blood flow to the loaded tissue. Tendon turns over slowly and has a poor blood supply, so getting precursors to it when flow is highest is the logic for taking the dose roughly 30 to 60 minutes before loading rather than at any other time (Shaw et al. 2017).
The key evidence
The proof-of-concept study took eight healthy men and gave them placebo, 5 g or 15 g of vitamin-C-enriched gelatin an hour before a short bout of rope-skipping. The 15 g dose roughly doubled a blood marker of collagen synthesis (the amino-terminal propeptide of collagen I) over placebo, and serum drawn after that dose increased both the collagen content and the mechanical strength of an engineered ligament in the lab, in a dose-dependent way (Shaw et al. 2017). That is a clean mechanistic result: the precursors reach the blood, synthesis markers rise, and engineered tissue responds.
What follows from there is less clean. A systematic review of eight controlled trials pairing collagen with resistance or plyometric training found that several reported real gains in tendon cross-sectional area and stiffness in favour of collagen, while the rest showed only the same directional trend or training-driven gains with no clear difference from placebo (Buchalski et al. 2026). The trials are small, almost entirely male, short, and run in lifters rather than distance runners. Direct trials measuring injury rates or tendon stiffness in running populations are essentially absent. The blood-marker and engineered-tissue findings are a long way from a proven drop in real-world tendon and bone injuries.
The verdict
Timed collagen or gelatin with vitamin C is biologically plausible, cheap and low-risk, and has promising early data for tendon structure and a coherent mechanism for bone too, where collagen is the scaffold that mineral is laid onto and where adequate vitamin D and calcium matter more. A reasonable protocol from the existing work is around 15 g of gelatin or hydrolysed collagen with a source of vitamin C, taken 30 to 60 minutes before loading or rehab work. It is most defensible as an adjunct during tendon or bone-stress rehabilitation, or for runners with a history of connective-tissue trouble, rather than as a general performance aid. It does not replace the things that move the needle most for tissue health: progressive loading, adequate total protein, enough energy and the unglamorous basics. Promising, not proven.