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Proline

Supplement amino acid general nutrition
Aka: L-proline
Brands seen in Singapore: California Gold Nutrition, NOW Foods, Source Naturals, Vitacost, Nutricost
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
The main amino acid of collagen · few human trials
Pros & cons
Pros
  • Proline and hydroxyproline are richest in collagen
  • Whole-body needs are the highest of any amino acid
  • Humans can make it from arginine and glutamate
Cons
  • The dose-response work read is in pigs, not people
  • No human skin or hair trial found in 1,163 hits
  • Synthesis falls short only in neonates, birds and fish
Sources
  1. Proline and hydroxyproline metabolism: implications for animal and human nutrition (Wu et al., Amino Acids 2011; PMC3773366) · read 2026-08-27
    what it says
    “On a per-gram basis, proline plus hydroxyproline are most abundant in collagen and milk proteins, and requirements of proline for whole-body protein synthesis are the greatest among all amino acids.”
  2. Wu et al., Amino Acids 2011 — physiological roles · read 2026-08-27
    what it says
    “Proline plays important roles in protein synthesis and structure, metabolism … as well as wound healing, antioxidative reactions, and immune responses.”
  3. Wu et al., Amino Acids 2011 — endogenous synthesis · read 2026-08-27
    what it says
    “While most mammals (including humans and pigs) can synthesize proline from arginine and glutamine/glutamate, rates of endogenous synthesis are inadequate for neonates, birds, and fish.”
  4. Wu et al., Amino Acids 2011 — dose-response data are in pigs and chickens · read 2026-08-27
    what it says
    “work with young pigs … has shown that supplementing 0.0, 0.35, 0.7, 1.05, 1.4, and 2.1% proline to a proline-free chemically defined diet … dose dependently improved daily growth rate and feed efficiency”
  5. Europe PMC REST search, 27 Aug 26 — proline in title plus supplementation/collagen/human/metabolism/nutrition (1,163 hits; the first pages are tumour metabolism, plant biology and livestock feeding, with no human supplementation trial and no human skin or hair outcome) · read 2026-08-27
    what it says
    “"hitCount":1163 … "Dietary Proline Supplementation Promotes Growth and Development in Weaned Foals by Modulating Gut Microbial Amino Acid Metabolism."”
  6. HSA Health Supplements Guidelines GL-CHPB-3-001 Rev. No. 020 (January 2026) — s3.1 working definition and clause 4.8 (Tables 4-5 cover vitamins and minerals only) · read 2026-08-27
    what it says
    “Vitamins, minerals, amino acids, fatty acids, enzymes, probiotics and other bioactive substances … HS for use by the general adult population should not contain vitamins and minerals exceeding the stipulated limits stated in Tables 4 and 5.”
  7. HSA Guidelines on Prohibited and Restricted Ingredients in HS and TM, GL-CHPB-1-012 Rev. No. 001 (Oct 2025), Annex A/B — full text searched 27 Aug 26, no row for proline · read 2026-08-27
    what it says
    “The objective of this guideline is to highlight the substances of concern when used in HS and TM and is not meant to be an exhaustive list.”
  8. iHerb Singapore category page "L-Proline", default best-selling order, first 5 distinct brands · read 2026-08-27
    what it says
    “L-Proline”
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Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.