Limited evidenceJoints & skin

L-Proline

An amino acid that makes up a large share of collagen, sold on that basis for skin and joints. No trial has ever tested isolated L-proline; the evidence comes from proline-rich proteins like gelatin and collagen peptides.

Evidence last reviewed: August 2026

What the science says

Isolated L-proline Limited evidence
No randomized controlled trial of L-proline supplementation alone for skin, tendon or joint outcomes is indexed in PubMed. Proline is also non-essential, meaning the body synthesises it, so deficiency is not a realistic problem on an adequate diet.
Proline-rich protein sources Limited evidence
A randomized trial found that vitamin C-enriched gelatin taken before intermittent exercise increased a blood marker of collagen synthesis, and a dose-comparison randomized trial found the collagen synthesis response was greater with 30 g of hydrolysed collagen than with 15 g or none. Both measured short-term blood markers, not skin appearance or joint symptoms, and both used whole proteins rather than free proline.
Vitamin C dependence Limited evidence
Proline only becomes structurally useful in collagen after hydroxylation, a reaction that requires vitamin C. This is well-established biochemistry, but it is an argument for adequate vitamin C rather than evidence that extra proline helps.

Dosage & safety

Studied doseNo studied dose for isolated L-proline; labels typically suggest 500–1,000 mg/day. Trials of proline-rich alternatives used 15–30 g/day of gelatin or hydrolysed collagen.

SafetyFree amino acid supplements at label doses are generally well tolerated. High single doses of individual amino acids can compete with others for absorption and transport. People with kidney or liver impairment should not take concentrated amino acid supplements without medical advice.

Scientific references

Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis
Shaw G, Lee-Barthel A, Ross ML — Am J Clin Nutr, 2017
The Collagen Synthesis Response to an Acute Bout of Resistance Exercise Is Greater when Ingesting 30 g Hydrolyzed Collagen Compared with 15 g and 0 g in Resistance-Trained Young Men
Lee J, Tang JCY, Dutton J — J Nutr, 2024

Where to buy

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