Probiotics may help lift mood

Daily intake of multispecies probiotics confers mood-improving benefits, reducing the processing of negative emotional cues and drawing attention to positive emotional stimuli, among others, as shown in a recent study.

In a cohort of 71 individuals (mean age 28.8 years, 63.4 percent women) with moderate depression who participated in a 4-week intervention, probiotic supplementation resulted in more accurate identification of faces expressing a particular emotion (difference, 12 percent; p<0.05) on the facial expression recognition task (FERT) relative to placebo. [Psych Med 2022;doi:10.1017/S003329172100550X]

Moreover, those who received probiotics exhibited increased vigilance to neutral faces (mean difference between groups, 12.28 ms; p<0.05) on the dot-probe task, meaning they paid less attention to happy and fearful emotions as compared with individuals who received placebo.

Meanwhile, on the probabilistic instrumental learning task (PILT), the probiotic group was less likely to select both the high-probability wins and the low-probability losses than the placebo group (difference, −9 percent; p<0.05), which was indicative of reduced reward learning. In terms of cognitive performance, the probiotic group also had reduced interference word recall on the auditory verbal learning task (AVLT; difference, −18 percent; p<0.05).

Probiotic supplementation produced no meaningful effects on sleep, salivary cortisol, or circulating C-reactive protein concentrations. However, it significantly reduced depression scores on the Patient Health Questionnaire-9 (PHQ-9; −50 percent from baseline; p<0.05), but this did not correlate with the changes in emotional processing.

In a different way

“Taken together these data suggest that the intake of this probiotic alters emotional processing in moderately depressed people in a different way to that previously reported with conventional antidepressant treatments,” according to the investigators.

Antidepressants work by reducing negative bias towards emotionally salient cues and/or increasing bias towards positive affective information, they said. In contrast, the probiotic helps increase perception and attention towards nonemotional cues, as reflected by the greater accuracy at identifying all emotions on the FERT and reduced vigilance to both positive and negative cues on the dot-probe task. [Psychopharmacology 2021;238:1265-1278]

The investigators also noted that while probiotic seems to reduce sensitivity to both win and loss outcomes, antidepressants have been reported to increase win responses.

It is possible that the impact of probiotic is limited to the cognitive processes that discern emotion-weighted outcomes in attention and learning, they pointed out. “Thus, probiotic could be said to convey some degree of emotional impartiality where [individuals] are less sensitive to specific emotional stimuli or are less influenced by losses and wins,” they said.

In light of the evidence, probiotic administration may be given as an early intervention strategy to reduce the risk of people with mild-to-moderate depression developing a major depressive disorder, according to the investigators.

“Further work is required to test the duration of the beneficial effects of the current probiotic at the levels of emotional processing, mood, and metabolism,” they added.