Influence of Probiotic and Conventional Yoghurt on the Status of Vitamins B<sub>1</sub>, B<sub>2</sub> and B<sub>6 </sub>in Young Healthy Women

<i>Background:</i> In vitro studies indicate that yoghurt bacteria are able to generate several water-soluble vitamins and therefore yoghurt could be a good source of these micronutrients. However, whether lactobacilli or other viable bacteria release the synthesized vitamins or utilize vitamins from their surroundings is a matter of debate. This study was carried out to investigate whether probiotic and traditional yoghurt bacteria are able to influence the status of different B vitamins (B₁, B₂, B₆) in young healthy women. <i>Methods:</i> In this investigation, female volunteers consumed 100 g/day of probiotic (n = 17) or conventional yoghurt (n = 16) for 2 weeks (T1–T2) and 200 g/day for another 2 weeks (T2–T3). A wash-out phase lasting 2 weeks followed. Plasma and urine concentrations of thiamine (vitamin B₁), riboflavin (B₂) and pyridoxine (B₆) were analyzed using HPLC. The functional parameters, i.e. the erythrocyte transketolase (α-ETK) expressed as TPP (thiamine pyrophosphate) effect, erythrocyte glutathione reductase (α-EGR) and glutamic oxaloacetic transaminase (α-EGOT) were determined photometrically. <i>Results:</i> The plasma levels of vitamin B₁ increased significantly in both the probiotic (p < 0.001) and the control group (p < 0.01) when consuming 200 g yoghurt/day (T2–T3) and decreased to the baseline levels after the wash-out phase (T3–T4). Urinary excretion of thiamine and the TPP effect did not significantly change in either the probiotic or the control group during the period of daily yoghurt consumption (T1–T3). The plasma concentration of flavin adenine dinucleotide (FAD) decreased significantly (p < 0.001) after consuming 100 g yoghurt/day (T1–T2) while plasma concentrations of flavin mononucleotide (FMN) (probiotic: p < 0.01, control: p < 0.001) and free riboflavin increased significantly (probiotic: p < 0.01, control: p < 0.001). Afterwards, the levels of these parameters remained unchanged to the end of the study in both tested groups. The urinary excretion of riboflavin and α-EGR remained unaffected throughout the study in both the probiotic and the control group. The average status of vitamin B₆, evaluated by its plasma level, urinary excretion and α-EGOT was unaffected by daily intake of 100 g (T1–T2) and 200 g yoghurt (T2–T3), respectively, for 4 weeks (T1–T3). <i>Conclusion:</i> The results of the present study indicate that daily consumption of 200 g of both, probiotic and conventional yoghurt for 2 weeks can contribute to the total intake of vitamin B₁ and B₂ reflected by increased levels of plasma thiamine and free riboflavin in healthy women. The diminished plasma FAD and increased FMN concentrations, observed during the period of daily yoghurt consumption in both groups, may be the result of enhanced immune function and an oxidant/antioxidant imbalance, caused by the daily intake of lactic acid bacteria. Since the long term status parameters of all three investigated vitamins (B₁, B₂, B₆) remained unaffected during the investigation the changes in plasma concentrations seem more likely the result of regular yoghurt consumption as a fermented dairy product, rather than of the specific intake of probiotic bacteria.