Collagen Peptides Guide: Effects on Joints, Skin, and Tendons — and Why Vitamin C Matters

Collagen is the most abundant protein in the body, comprising approximately 30% of all proteins, and is the primary structural component of tendons, ligaments, cartilage, skin, bone, and blood vessels. It is composed of the amino acids hydroxyproline, proline, and glycine, forming a tropocollagen structure where three polypeptide chains intertwine in a helix. Collagen synthesis declines with age (starting around age 25), contributing to cartilage wear, skin sagging, and reduced tendon flexibility. Collagen peptide supplements are collagen that has been digested and hydrolyzed into low-molecular-weight peptides.

~30%

Collagen's proportion of total body protein

An RCT by Shaw et al. (2017) showed that consuming 15g of collagen peptides (with vitamin C) one hour before exercise significantly improved collagen content and mechanical properties in a tendon tissue engineering model. Blood levels of collagen precursors (glycine, proline, hydroxyproline) also rose after intake, suggesting enhanced collagen incorporation into tendons and ligaments. For joint pain, there are also RCTs showing that 10g/day of collagen peptides produces significant improvement in knee joint pain in physically active individuals. Cartilage protection effects are also being studied, with promotion of cartilage collagen synthesis expected.

1 hour before

Optimal timing before exercise for enhanced effect

10–15 g/day

Dose commonly used in research

Evidence for skin effects of collagen peptides has accumulated across multiple RCTs and meta-analyses. Oral intake of specific hydrolyzed collagen peptides has been shown to contribute to improvements in skin elasticity, moisture retention, and wrinkle reduction, attracting attention in the fields of dermatology and aesthetic medicine. Continued use of approximately 8–12 weeks is typically needed before effects are seen. Note that the mechanism differs from topical collagen creams — oral collagen peptides work through a pathway where, after digestion and absorption, they stimulate collagen production throughout the body.

8–12 weeks

Approximate duration needed for skin effects

There is a clear reason why vitamin C is indispensable for collagen synthesis. The enzymes that hydroxylate the amino acids proline and lysine (prolyl hydroxylase and lysyl hydroxylase — converting them to hydroxyproline and hydroxylysine) require vitamin C as a cofactor. Without this step, the stable triple helix structure of collagen cannot form. The RCT by Shaw et al. demonstrated effects in vitamin C-added groups, and co-ingesting vitamin C (50+ mg recommended) when taking collagen peptides improves synthesis efficiency.

Collagen is also found in animal foods (chicken skin, beef tendon, fish skin, bone broth, etc.), but dietary collagen is broken down into amino acids before absorption and is theoretically indistinguishable from amino acids from other protein sources. In contrast, collagen peptide supplements are absorbed in the form of low-molecular-weight peptides (dipeptides and tripeptides) after hydrolysis, and are detected in the blood as peptides such as prolyl-hydroxyproline (Pro-Hyp). The pathway by which these peptide forms stimulate fibroblasts to enhance collagen production is under research. The difference from dietary sources is thought to lie in the form of absorption and efficiency of delivery to target tissues.