MuscleLedger

Collagen and Vitamin C: Why the Trials Put Vitamin C in Every Arm, and What Labels Add

Vitamin C is required to build collagen, which is why the exercise trials of collagen and gelatin add it to the drink — but they put it in the placebo too, so none tests what vitamin C adds. The amounts used were 40–50 mg. Of 223 on-market collagen-peptide powder labels, 38 list vitamin C, at a median of 90 mg. At 500 mg and above, with vitamin E, two training trials found blunted adaptations.

Leon H · Edited by Caroline S · Published 2026-10-22

Illustration: An unbranded glass bottle of vitamin C tablets on a wooden bench with a towel in a locker room.
Illustration

"Take collagen with vitamin C" is one of the most repeated lines about collagen supplements, and it rests on solid biochemistry: without vitamin C, the body cannot finish building collagen. What the line skips is that the human trials of collagen for tendons and ligaments were not designed to test vitamin C at all. They put it in every drink, including the placebo.

This page covers the vitamin C question. The timing of collagen around exercise is on best time to take collagen, collagen for joints on collagen for joints, and the tendon research on peptides for joints and tendons.

Why vitamin C matters to collagen

Collagen is made as a long precursor chain, procollagen. Before it can fold into its rope-like triple helix, enzymes add hydroxyl groups to many of its proline units — and that step needs ascorbate (vitamin C) to work. Hydroxyproline is what holds the triple helix stable. Without enough vitamin C, procollagen is under-hydroxylated and poorly secreted, and connective tissue weakens; that is the mechanism behind the bleeding gums and failed wound healing of scurvy (Peterkofsky, American Journal of Clinical Nutrition, 1991).

That makes vitamin C a requirement for collagen synthesis. It does not by itself mean that adding more vitamin C to a collagen drink increases synthesis in someone who already has enough. The same 1991 review noted that in vitamin C-deficient guinea pigs, collagen synthesis fell with only moderate effects on proline hydroxylation, in step with the animals' weight loss — the deficiency acts through more than the one enzyme step.

What the trials actually tested

The "vitamin C-enriched collagen" idea comes from Keith Baar's laboratory. Reading the methods sections shows how vitamin C was handled:

Trial Collagen arms Vitamin C What was compared
Shaw et al. 2017 (8 men) 0, 5 or 15 g gelatin 48 mg in every arm (80 mL blackcurrant cordial) Gelatin dose against a constant vitamin C background
Lis and Baar 2019 (10 men) Placebo, 15 g gelatin, hydrolysed collagen or a gummy "Vitamin C-enriched" supplements Collagen forms
Lee et al. 2024 (10 young men) 0, 15 or 30 g hydrolysed collagen 50 mg in every arm Collagen dose against a constant vitamin C background
Nulty et al. 2024 (8 middle-aged men) 0, 15 or 30 g hydrolysed collagen "Vitamin C-enriched" (amount not stated in the abstract) Collagen dose

The figures are as each trial reports them; none of them is a recommendation.

In Shaw and in Lee, the zero-collagen drink contained the same vitamin C as the collagen drinks. Those designs answer "does adding collagen to a vitamin C drink raise collagen synthesis?" — 15 g of gelatin doubled the synthesis marker in Shaw; only 30 g beat the 0 g drink in Lee — but they cannot answer "does adding vitamin C to collagen help?", because vitamin C never varied. The results by dose are set out on best time to take collagen, and the muscle-tissue measurements on collagen peptides for muscle recovery.

One trial went the other way on vitamin C and found no effect of collagen. A 2023 Maastricht trial gave 45 recreational athletes 30 g of collagen, 30 g of whey or placebo after exercise, with no vitamin C, and measured muscle connective-tissue synthesis directly by biopsy: no significant difference between groups. The Liverpool authors of the 2024 trial list the missing vitamin C as one of several design differences that might explain the disagreement. It is a hypothesis, not a finding — nobody has run the same protocol with and without vitamin C.

The registered tendon trial

The first large randomised trial of collagen with vitamin C for a tendon condition, the Dutch JUMPFOOD study of patellar tendinopathy ("jumper's knee"), gives 10 g of hydrolysed collagen with 40 mg of vitamin C daily for 24 weeks alongside a tendon-loading programme, against a maltodextrin placebo, in 76 athletes. Its protocol was published in 2023 (NCT05407194). On 2026-10-22 ClinicalTrials.gov listed its status as unknown, with an estimated completion date of May 2026 and no results posted. Its placebo carries no vitamin C, so even when it reports it will test the combination, not vitamin C's share.

How much vitamin C collagen products add

MuscleLedger searched the NIH Office of Dietary Supplements' label database (DSLD) on 2026-10-22 for on-market powders named "collagen peptides": 223 labels.

Labels
List vitamin C as an ingredient 38 of 223
State an amount 33
— median per serving 90 mg
— most common amount 90 mg (12 labels)
— range 45–500 mg

Labels count printings, not products: some brands appear several times for different flavours. For scale, the US recommended dietary allowance for adults is 90 mg a day for men and 75 mg for women, with 35 mg more for smokers, and intakes above 2,000 mg a day are not recommended (MedlinePlus, US National Library of Medicine). So the typical label adds about a man's daily allowance, roughly double what the trials used.

The high-dose caveat

Vitamin C is an antioxidant, and at high doses, combined with vitamin E, it has blunted training adaptations in two Norwegian trials:

  • Paulsen et al. 2014: 54 young adults, 1,000 mg vitamin C + 235 mg vitamin E daily for 11 weeks of endurance training. VO2max improved equally, but mitochondrial markers in muscle (COX4, PGC-1α) rose on placebo and not on the vitamins.
  • Bjørnsen et al. 2016: 34 men aged 60–81, 500 mg vitamin C + 117.5 mg vitamin E before and after each session for 12 weeks of strength training. Total lean mass rose 3.9% on placebo and 1.4% on the vitamins; rectus femoris thickness rose 16.2% against 10.9%; strength gains did not differ.

The figures are as each trial reports them; none of them is a recommendation. These trials combined two antioxidants at doses several times higher than collagen products contain; they do not show that 50–90 mg of vitamin C alongside collagen does any harm. They are the reason "more vitamin C is better" is not a safe assumption for people who train.

What is not established

  • Whether adding vitamin C to collagen changes collagen synthesis in people with adequate vitamin C intake. No trial has varied vitamin C while holding collagen constant.
  • Whether any collagen-plus-vitamin C product improves an injury outcome. The first large tendinopathy trial has not reported.
  • The right amount, if any. The trials used 40–50 mg; labels use a median of 90 mg; neither figure was chosen by a dose-finding study.

Tendon and ligament injuries, and questions about vitamin supplements alongside medication, belong with a clinician or sports-medicine physiotherapist.

Sources

All opened 2026-10-22.

  • Peterkofsky B. "Ascorbate requirement for hydroxylation and secretion of procollagen: relationship to inhibition of collagen synthesis in scurvy." Am J Clin Nutr 1991;54(6 Suppl):1135S–1140S. PMID 1720597
  • Shaw G, Lee-Barthel A, Ross ML, Wang B, Baar K. "Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis." Am J Clin Nutr 2017;105(1):136–143 (full text, methods). PMID 27852613
  • Lis DM, Baar K. "Effects of Different Vitamin C-Enriched Collagen Derivatives on Collagen Synthesis." Int J Sport Nutr Exerc Metab 2019;29(5):526–531. PMID 30859848
  • Lee J et al. "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." J Nutr 2024;154(7):2076–2086 (full text, methods and discussion). PMID 38007183
  • Nulty CD et al. "Hydrolyzed collagen supplementation prior to resistance exercise augments collagen synthesis in a dose-response manner in resistance-trained, middle-aged men." Am J Physiol Endocrinol Metab 2024;327(5):E668–E677. PMID 39259166
  • Aussieker T et al. "Collagen Protein Ingestion during Recovery from Exercise Does Not Increase Muscle Connective Protein Synthesis Rates." Med Sci Sports Exerc 2023;55(10):1792–1802. PMID 37202878
  • van Dam L et al. "The JUMPFOOD study: additional effect of hydrolyzed collagen and vitamin C to exercise treatment for patellar tendinopathy." Trials 2023;24(1):768. PMID 38017500; registry status from ClinicalTrials.gov NCT05407194, read 2026-10-22.
  • Paulsen G et al. "Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans." J Physiol 2014;592(8):1887–901. PMID 24492839
  • Bjørnsen T et al. "Vitamin C and E supplementation blunts increases in total lean body mass in elderly men after strength training." Scand J Med Sci Sports 2016;26(7):755–63. PMID 26129928
  • MedlinePlus, "Vitamin C" (recommended intakes and the 2,000 mg line), US National Library of Medicine. medlineplus.gov/ency/article/002404.htm
  • NIH Office of Dietary Supplements, Dietary Supplement Label Database API v9: search "collagen peptides", on-market powders named "collagen peptides" (223), vitamin C rows read from 38 labels, queried 2026-10-22. dsld.od.nih.gov

Frequently asked questions

Does collagen need vitamin C to work?

The body needs vitamin C to build collagen — the enzymes that finish collagen molecules depend on it, which is why scurvy damages connective tissue. Whether adding vitamin C to a collagen supplement changes anything in a person who already gets enough vitamin C from food has never been tested: the exercise trials gave vitamin C to every group, including placebo.

How much vitamin C was used with collagen in the studies?

The exercise trials used 48 mg (Shaw 2017, in a blackcurrant cordial) and 50 mg (Lee 2024 and Nulty 2024), and a registered tendon trial uses 40 mg a day. These are the amounts studied, not guidance. For comparison, the US recommended daily intake for adults is 90 mg for men and 75 mg for women.

Should collagen and vitamin C be taken at the same time?

The trials gave them in the same drink, about an hour before exercise, but none compared same-time with separate-time intake, or collagen with and without vitamin C. The timing evidence is set out on this site's best-time-to-take-collagen page. Vitamin C from food over the day also counts toward the body's supply.

Is it worth buying collagen with added vitamin C?

The trials cannot answer that: they show collagen doses with vitamin C in the background, not the effect of the vitamin C itself. Of 223 collagen-peptide powder labels checked, 38 add vitamin C at a median of 90 mg per serving — about one day's recommended intake for a man. Someone eating fruit and vegetables daily is unlikely to be short of vitamin C, but no trial has tested the label combination directly.

Can too much vitamin C interfere with training?

At high doses combined with vitamin E, two Norwegian trials found it may: 1,000 mg of vitamin C with 235 mg of vitamin E blunted mitochondrial markers after endurance training, and 500 mg of vitamin C with 117.5 mg of vitamin E around each session blunted lean-mass gains in older men. The amounts in collagen products and collagen trials are far lower. MedlinePlus advises against more than 2,000 mg of vitamin C a day.