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Can Probiotics Treat Depression?

November 30, 2013

Preclinical data strongly support conducting clinical studies of probiotics to treat depression, according to a review article in the November Biological Psychiatry. 

Timothy G. Dinan, MD, PhD, and colleagues from the University College Cork in Ireland, defined a class of probiotics, called psychobiotics, as “a live organism that, when ingested in adequate amounts, produces a health benefit in patients suffering from psychiatric illness.” 

Dr. Dinan notes that the human gut microbiota contains about 1 kg of bacteria and is home to more than 7000 strains of microorganisms. The microbiota is a dynamic environment that diet and other factors can affect from birth onward. 

Evidence links depression and stress with inflammation in the body, and researchers have hypothesized that the major classes of antidepressants may work by suppressing inflammation. “The intestinal microbial balance may alter the regulation of inflammatory responses and in doing so may be involved in the modulation of mood and behavior,” the authors stated. 

Although more human studies are needed, a recent double-blind, placebo-controlled, randomized parallel group study showed promising results. Participants received either a probiotic combination of L. helveticus R0052 and B. longum or placebo for 30 days. Those who received the probiotic combination reported less psychological distress and showed reduced levels of urinary cortisol. 

Another human study compared mood and cognition in 124 participants receiving either a daily probiotic-containing milk drink or placebo. Participants with baseline mood in the lowest third reported as happy rather than depressed after consuming the probiotic. 

In an animal study of the potential benefits of the probiotic B. infantis, rats exhibiting depressive behavior after separation from their mothers were treated with B. infantis or citalopram, a selective serotonin reuptake inhibitor (SSRI). The probiotic treatment was linked with normalized behavior and immune response. 

Considering the available preclinical evidence, Dr. Dinan and colleagues support undertaking clinical studies with probiotics in depression. However, they caution that not all probiotics are likely to have psychobiotic potential. 

“Numerous putative probiotics studied in our laboratory were found to have no demonstrable impact on behavior. To detect psychobiotics, we would favor probiotic strains that preclinically have shown behavioral effects, are delivery vehicles for neuroactive compounds, and have a capacity to decrease proinflammatory cytokines and reduce HPA activity,” they wrote. 

The authors suggest that researchers examine data from studies of irritable bowel syndrome and probiotics, as these data may help determine which subtype of depression is most likely to respond to probiotics. 

“An in-depth analysis of the microbiota in depression and other stress-related disorders needs to be undertaken. The preclinical data strongly support the view that an aberrant microbiota can alter behavior, immunity, and endocrinology,” the study authors wrote. 

—Lauren LeBano 


1. Dinan TG, Stanton CS, Cryan JF. Psychobiotics: A novel class of psychotropic. Biological Psychiatry. 2013;74(10:720-726.

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