The Effect of Vitamin C Supplementation on Gut Microbiota Composition and Function in Healthy Adults

NCT07388121 | Recruiting

• 1 other identifier: 200250024
• Study Type: interventional
• Target: 23
• Locations: 1 country
• Sites: 1

Brief Summary

The aim of this dietary intervention study is to explore how vitamin C affects the bacteria that live in our gut. Vitamins are essential nutrients found in fruits and vegetables. Our bodies cannot make them on their own, but we need them to function correctly. Vitamins play various roles, including supporting the immune system and assisting with energy production. Some vitamins in our diet can reach the large intestine, where they may be used by gut bacteria to promote their growth. In this study, we aim to investigate how our gut bacteria interact with vitamin C and how this interaction affects their growth and activity. For this study, participants will follow their habitual diet for one-week (run-in period), followed by two consecutive two-week supplementation periods in which they will first take a moderate dose (200 mg/day) and then a high-dose (1000 mg/day) of vitamin C. A final one-week period follow up period will involve a return to their habitual diet. Faecal, blood and urine samples will be collected at the start and end of each supplementation period to explore changes in gut microbiota composition, activity and markers of inflammation.

Conditions

Gut Microbiota Diversity and Composition; Short Chain Fatty Acids Concentration in Stools

Keywords

vitamin C; gut microbiota; SCFA

Outcome Measures

Primary Outcomes (3)

• Butyrate (Short Chain Fatty Acid)

  Quantified in stool samples using Gas Chromatography

  Baseline (Visit 1), Week 1 (Visit 2), Week 3 (Visit 3), Week 5 (Visit 4) and Week 6 (Visit 5)

• Short Chain Fatty Acids i.e. acetate, propionate, butyrate, total

  Quantified in stool samples using Gas Chromatography

  Baseline (Visit 1), Week 1 (Visit 2), Week 3 (Visit 3), Week 5 (Visit 4) and Week 6 (Visit 5)

• Stool microbiota composition analysis

  16S rRNA gene amplicon sequencing from faecal DNA extracts

  Baseline (Visit 1), Week 1 (Visit 2), Week 3 (Visit 3), Week 5 (Visit 4) and Week 6 (Visit 5)

Secondary Outcomes (3)

• Stool pH

  Baseline (Visit 1), Week 1 (Visit 2), Week 3 (Visit 3), Week 5 (Visit 4) and Week 6 (Visit 5)

• Vitamin C in plasma

  Week 1 (Visit 2), Week 3 (Visit 3), and Week 5 (Visit 4)

• Inflammatory markers

  Week 1 (Visit 2), Week 3 (Visit 3), and Week 5 (Visit 4)

Other Outcomes (1)

• Gut barrier function markers

  Week 1 (Visit 2), Week 3 (Visit 3), and Week 5 (Visit 4)

Study Arms (1)

Sequential vitamin C intervention

EXPERIMENTAL

In this single-arm, sequential dietary intervention study, participants will follow their normal habitual diet for one week (run-in period) and then receive two different doses of vitamin C tablets over two consecutive 14-day periods: a moderate dose of 200 mg/day during the first period (2 weeks) and a high dose of 1000 mg/day during the second period (another 2 weeks). The study also includes one week post intervention follow up period (habitual diet) after the high vitamin C dose where participants return to their habitual diet without vitamin C supplementation

Dietary Supplement: Moderate Vitamin C dose (200 mg); Dietary Supplement: High-dose vitamin C supplementation (1000 mg); Other: Habitual diet (run in period)

Interventions

Moderate Vitamin C dose (200 mg) DIETARY_SUPPLEMENT

200 mg of vitamin C provided as a chewable tablet, taken orally daily for two weeks

Sequential vitamin C intervention

High-dose vitamin C supplementation (1000 mg) DIETARY_SUPPLEMENT

1000 mg of Vitamin C provided as a chewable tablet, taken orally daily for two weeks

Sequential vitamin C intervention

Habitual diet (run in period) OTHER

this is a run-in period where participants consume their habitual diet for one week

Sequential vitamin C intervention

Eligibility Criteria

• Age: 18 Years - 65 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• Healthy individuals aged 18-65 years with a BMI between 18.5-35 Kg/m2
• Self-reported good health with no chronic conditions requiring regular medical care
• Willing to provide blood, urine, and stool samples at multiple time points

You may not qualify if:

• Aged \<18 or \>65 years
• Smoking
• Chronic illness requiring regular medication or GP visits
• Current or recent medication affecting gut transit or digestion
• Major gastrointestinal surgery
• Pregnant or breastfeeding
• Regular use of pre/probiotics, vitamins, or minerals (unless willing to discontinue 2-4 weeks prior)
• Antibiotics in past 3 months
• Weight change \>±2 kg in past month
• Participation in other research likely to interfere with this study

Sponsors & Collaborators

• University of Glasgow: lead
• Professor Konstantinos Gerasimidis, University of Glasgow: collaborator

Study Sites (1)

New Lister Building, Glasgow Royal Infirmary, 10-16 Alexandra Parade, G31 2ER

Glasgow, G31 2ER, United Kingdom

RECRUITING

MeSH Terms

Interventions

Jogging

Intervention Hierarchy (Ancestors)

Running; Locomotion; Movement; Musculoskeletal Physiological Phenomena; Musculoskeletal and Neural Physiological Phenomena; Exercise; Motor Activity

Study Officials

• Athanasios Koutsos, PhD

  Human Nutrition, School of Medicine, College of Medical, Veterinary, and Life Sciences, University of Glasgow

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Raihana Halim

CONTACT

07857 725347; 2859495H@student.gla.ac.uk

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: NON RANDOMIZED
• Masking: NONE
• Purpose: BASIC SCIENCE
• Intervention Model: SEQUENTIAL
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Lecturer in Human Nutrition

Study Record Dates

• First Submitted: December 18, 2025
• First Posted: February 4, 2026
• Study Start: November 1, 2025
• Primary Completion (Estimated): July 1, 2026
• Study Completion (Estimated): July 1, 2026
• Last Updated: February 4, 2026

Record last verified: 2025-11

Locations

GB (1)