Probiotics, either taken alone or combined with prebiotics, may help to ease depression, suggests a review of the available evidence published in BMJ Nutrition Prevention & Health.
Researchers at Brighton and Sussex Medical School conducted a systematic review of databases and grey literature sites to investigate pre- and/or probiotics as treatments for depression and/or anxiety disorders. Only research published in the last 15 years was included.
Seven eligible studies were identified. All seven studies investigated at least one probiotic strain; three studies investigated a single probiotic strain, whereas four studies investigated the effect of multiple probiotic strains as a combined intervention.
A total of 12 strains were investigated; most commonly tested were Lactobacillus acidophilus, Lactobacillus casaei and Bifidobacterium bifidium. One study investigated combined prebiotic-probiotic therapy, and one article investigated isolated prebiotic therapy.
The seven included studies demonstrated significant improvements in one or more measure of psychiatric conditions.
A probiotic alone or combined with prebiotic therapy significantly reduced 17 item Hamilton Depression Rating Scale and Beck Depression Inventory II scores in six of seven studies. There were no significant effects on depression and anxiety symptoms with the Symptom Checklist-90 and Perceived Stress Scale-10.
The findings indicate that, of the 12 different probiotics investigated, 11 are potentially useful agents, the authors say.
They conclude that the findings suggest pre-/probiotics may be a potentially useful adjunctive treatment for psychiatric conditions. They theorise that patients with certain co-morbidities, such as irritable bowel syndrome, might experience greater benefits from such treatments, given that pre-/probiotics are useful treatments for other conditions that were not the primary focus of this discourse.
However, it must be noted that the findings are limited by several factors: adequate though not robust sample sizes, short study durations, long-term effects and propensity for remission.