In a small pilot study of men with schizophrenia, researchers at Johns Hopkins Medicine and Sheppard Pratt Health System say they have evidence that adding probiotics to the patients’ diets may help treat yeast infections and ease bowel problems. Probiotics may also decrease delusions and hallucinations, but in the study, these psychiatric benefits mostly affected those without a history of yeast infections.

The findings, published in the May 1 issue of the journal Brain, Behavior, and Immunity, support growing evidence of close links between the mind and the gut.

The investigators caution that larger and more rigorous studies are needed to validate their findings and determine if women with schizophrenia respond similarly to probiotics before this fairly simple and cost–effective treatment strategy should be recommended widely to people with schizophrenia.

“The mental health field is in desperate need of new treatments for psychiatric disorders, yet there’s been very little progress toward this goal for too long a time. The tiny living organisms that make up the human microbiome and the overwhelming evidence for a gut–brain axis together represent a new frontier for schizophrenia research,” says Emily Severance, PhD, assistant professor of pediatrics and part of the Stanley Division of Developmental Neurovirology at the Johns Hopkins University School of Medicine.

This new analysis included 56 adult participants with an average age of 46. Nineteen participants were women, and 61 percent were white. At the start of the trial, each participant gave a blood sample and completed the Positive and Negative Syndrome Scale (PANSS) exam used for measuring a standard set of symptoms of schizophrenia.

Each participant took a placebo pill once per day with a meal for the next two weeks and then were split into groups so that neither the researchers nor the participants could tell who would be given a real probiotic or the placebo for the next 14 weeks.

The commercially available probiotic contained over 1 billion colony–forming units of Lactobacillus rhamnosus and Bifidobacterium animalis in each pill.

Using the blood samples, the researchers measured antibody levels to yeast Saccharomyces cerevisiae, known as brewer’s yeast, and Candida albicans, known to cause yeast infections, before and after the probiotic treatment. Both types of yeast are elevated in people with schizophrenia.

The researchers found Candida antibody levels decreased by 43 percent over time in the 22 men taking probiotics but saw only a 3 percent decrease of antibodies in the 15 men receiving the placebo. Eighteen men responded to the treatment with reduced antibody levels; four men didn’t respond to the treatment. Antibody levels for the brewer’s yeast didn’t change over the course of the study in the participants after probiotic treatment. A treatment effect wasn’t detected in the women because their starting Candida antibody levels were already much higher in those on the placebo than in those taking the probiotics, which the researchers attributed to the small sample size of the trial.

For the next analysis, the researchers focused on the men who had evidence of a yeast infection due to elevated Candida antibodies. The five men in the placebo group with Candida had more difficulty with bowel movements over time, with an average bowel score of 0.74, compared to the 10 men without evidence of infection, who had an average score of 0.19. Severance says these results are consistent with the group’s earlier 2014 analysis of bowel function, but the current study reinforces that Candida yeast contribute to bowel difficulties in men with schizophrenia.

In patients treated with probiotics, PANSS psychiatric symptom scores on positive symptoms improved the most — from an average of 18 down to 14.6 on their PANSS score after 13 weeks.