The relationship between diet, gut flora, and mental health has received increasing attention in scientific circles. A study published in Brain, Behavior, and Immunity shows that high-dose vitamin Csupplements when taken to correct a deficiency can improve mental vitality and mood in healthy individuals. The authors describe how vitamin C supplementation influences the gut microbiota, and how the balance of the gut flora is closely linked to mood through the so-called gut–brain–immune axis.