Vitamins are essential micronutrients for health (1). Recently, vitamins have gained recognition as potential modulators of the gut microbiota (2). However, the direct effects of individual vitamins on gut microbiota metabolic activity, including short chain fatty acid (SCFA) production, remain poorly understood. The aim of this study was to evaluate the in vitro effects of water-soluble (B-group and C), and fat-soluble (A, D, E, K) vitamins on the fermentation capacity of mixed fibres (MF) in an in vitro batch culture model.
Faecal samples from 12 healthy adults (female, n=7; mean ± SD, age 36 ± 7 years; BMI 25.5 ± 3.51 kg/m2) were used to inoculate individual batch cultures simulating colonic conditions (pH 7, 37°C, anaerobic). For each donor, separate batch culture fermentations were performed for each vitamin individually (A, D, E, K, C, B1, B2, B3, B5, B6, B7, B9, B12) as well as selected combinations: B1 – B7, B9+B12, an antioxidant mixture (A, B2, C, E), water-soluble vitamins, lipid-soluble vitamins and all vitamins combined. All fermentations were performed in the presence of a MF mixture (apple pectin, inulin (orafti), alpha cellulose, and high resistant maize starch (hi-maize), 200 mg each) and lasted for 24 h.
Vitamins were added at 200% of the Reference Nutrient Intake (RNI). SCFA were analysed using gas chromatography. Paired T-tests were performed to assess the effect of each individual vitamin or vitamin mixture on SCFA compared to MF alone (control). This study gained ethical approval by the University of Glasgow, College of Medical, Veterinary and Life Sciences (MVLS) Ethics Committee (Ref: 200240004).
Butyrate production significantly increased with vitamin C in the presence of MF (9.27 ± 2.02 µmol/ml; p < 0.001) compared to the control (MF alone, 6.59 ±1.61 µmol/ml). Similar increases in butyrate were observed with the antioxidant mixture, water-soluble vitamins and all vitamins combined (9.16 ± 2.36, 8.88 ± 2.23, 10.02 ± 2.19 µmol/ml, respectively; all p < 0.001). These treatments also led to modest reductions in acetate levels (22.12 ± 3.49 µmol/ml, p = 0.004, 21.46 ± 4.07 µmol/ml, p = 0.014, and 22.15 ± 4.04 µmol/ml, p = 0.028, respectively) compared to the control (23.77 ± 3.32 µmol/ml). Total SCFA concentrations remained unchanged across all vitamin treatments.
These preliminary findings suggest that vitamin C alone or as part of other vitamin mixtures may selectively enhance butyrate production. This effect may be mediated through a reduction in redox potential, creating a more favourable environment for butyrate- producing bacteria. These results need to be confirmed in vivo, and further research is required to understand the underlying mechanisms of vitamin-microbiota interactions.