Side by side

1. 1.Digestion breaks the peptides further, and small fragments such as proline-hydroxyproline appear in the blood within an hour of ingestion.
2. 2.These fragments are proposed to signal fibroblasts in the skin and chondrocytes in cartilage, weakly stimulating new collagen production.
3. 3.The effect size is small, and part of any measured benefit may simply reflect the extra protein and amino acids in the diet.
4. 4.Hydroxyproline and glycine, which collagen supplies in quantity, are the raw materials for the body's own collagen synthesis.

• Skin hydration, elasticity and wrinkles
• Osteoarthritis joint pain and stiffness
• Bone mineral density in postmenopausal women
• Tendon and ligament complaints
• Muscle mass and function in older adults

• Small improvements in skin hydration and elasticity in meta-analyses, typically after 8–12 weeks
• Modest reductions in joint pain scores in some osteoarthritis trials
• Effects on bone density are inconsistent across studies
• Most trials are small and several are industry-funded, which biases results toward benefit
• No effect on body composition or strength has been demonstrated convincingly

• Generally well tolerated
• Mild bloating or gastrointestinal discomfort in some people
• Allergic reactions in people sensitive to the source animal (fish, bovine, porcine)
• Supplements often include added vitamins or other ingredients that carry their own risks

Research context only. Published trials most often used 2.5–10 g per day for 8–24 weeks, taken orally as powder or drink. As a food supplement there is no standard regimen, and no evidence that higher intakes add benefit.

Research context only