Probiotics, Brain Structure and Psychological Variables

A double-blind RCT intervention study will be conducted to investigate the effect of a probiotic dietary supplement vs. a placebo, taken by healthy human participants (N = 60) for 28 consecutive days. Both substances are administered in doses of 4.4g (powder) per day. The probiotic dietary supplement used in the present study is a freely available product (in powder form) sold under the name of Vivomixx®. Per 4.4g the powder contains 450 billion bacteria, composed of eight bacterial strains: Lactobacilli (L. paracasei, L. plantarum, L. acidophilus and L.delbrueckii subsp. bulgaricus), Bifidobacteria (B. longum, B. infantis, B. breve), and Streptococcus thermophiles. This product was chosen, because a similar supplement with an identical composition of bacteria as Vivomixx® was found to be linked to hippocampal neurogenesis in mice. The placebo powder has a similar taste and consistency as the verum (Vivomixx®) powder, but contains no probiotic bacteria. First, participants will be screened online for eligibility (T0). Before and after the 28-day intake period, participants are asked to perform several cognitive tests and fill out questionnaires (T1, T2) at our laboratory (ca. 2 - 2.5 hours). Afterwards, blood samples will be drawn (ca. 5 minutes) and a magnet resonance tomography (MRT) session (ca. 1 - 1.5 hours) will be conducted, where participants will perform an object pattern separation task in the scanner (T1, T2). Furthermore, a follow-up after 2 months (T3), including the same assessments as at T1 and T2, will be conducted. During the intake period participants will fill out a brief questionnaire on a weekly basis, which includes an assessment of state depression and anxiety, defecation (control item to rule out adverse effects), recent (start of) intake of medication, recent (onset of) intake of antibiotics, and recent inter-current illness (e.g. influenza). In addition, participants will record their food intake (protocol) for one week (7 consecutive days) during the intake period.