Collagen peptides

Not all collagen is equal. Hydrolyzed peptides differ by molecular weight and peptide profile, and the trials that show benefit used specific preparations at specific doses — details most supplement labels skip entirely.

Which peptides were studied

The strongest signal comes from randomized trials in active people with activity-related knee pain. In a 12-week trial of 139 athletes, 5 g of specific collagen peptides (FORTIGEL) reduced pain during activity significantly more than placebo. An earlier 24-week trial of 147 varsity athletes using 10 g of collagen hydrolysate daily found the same direction of effect, largest in the knee-pain subgroup.

For tendon rather than cartilage, TENDOFORTE plus calf strengthening more than doubled the functional improvement of exercise alone in a small crossover trial in chronic Achilles tendinopathy.

Dose & timing

The trials used 5–10 g daily for at least 12 weeks. Timing may matter more than most labels admit: collagen-synthesis markers peak when ingestion precedes loading exercise by about an hour, which is the basis of the pre-training protocol described below.

The vitamin C pairing

Vitamin C is a required cofactor for collagen cross-linking. In the gelatin-timing study, 15 g of vitamin C–enriched gelatin taken one hour before six minutes of rope skipping doubled serum PINP, a marker of collagen synthesis. It was a tiny crossover study using a surrogate marker — promising mechanism, not proof of joint repair.

What this does not show

No collagen trial has demonstrated regrowth of articular cartilage on imaging. The randomized evidence supports less activity-related pain and better tendon-loading tolerance — meaningful, but a different claim. Nearly all trials involve manufacturer funding or affiliated authors, and the subjective endpoints are exactly the kind most vulnerable to placebo effects.