Multispecies probiotic administration reduces emotional salience and improves mood in subjects with moderate depression: a randomised, double-blind, placebo-controlled study

Abstract

Background: The potential antidepressant properties of probiotics have been suggested, but their influence on the emotional processes that may underlie this effect is unclear.

Methods: Depressed volunteers (n = 71) were recruited into a randomised double-blind, placebo-controlled study to explore the effects of a daily, 4-week intake of a multispecies probiotic or placebo on emotional processing and cognition. Mood, anxiety, positive and negative affect, sleep, salivary cortisol and serum C-reactive peptide (CRP) were assessed before and after supplementation.

Results: Compared with placebo, probiotic intake increased accuracy at identifying faces expressing all emotions (+12%, p < 0.05, total n = 51) and vigilance to neutral faces (mean difference between groups = 12.28 ms ± 6.1, p < 0.05, total n = 51). Probiotic supplementation also reduced reward learning (-9%, p < 0.05, total n = 51), and interference word recall on the auditory verbal learning task (-18%, p < 0.05, total n = 50), but did not affect other aspects of cognitive performance. Although actigraphy revealed a significant group × night-time activity interaction, follow up analysis was not significant (p = 0.094). Supplementation did not alter salivary cortisol or circulating CRP concentrations. Probiotic intake significantly reduced (-50% from baseline, p < 0.05, n = 35) depression scores on the Patient Health Questionnaire-9, but these did not correlate with the changes in emotional processing.

Conclusions: The impartiality to positive and negative emotional stimuli or reward after probiotic supplementation have not been observed with conventional antidepressant therapies. Further studies are required to elucidate the significance of these changes with regard to the mood-improving action of the current probiotic.

Keywords: Bifidobacteria; Lactobacilli; emotional memory; mood disorder.

Fig. 1.

Schematic of the experimental procedure to test the effects of a 28-day intake of placebo or a multispecies probiotic on emotional processing in people with moderate depression. PHQ-9, Patient Health Questionnaire-9; SCID-5, Structural Clinical Interview for the DSM-V Axis I Disorders; PANAS, Positive And Negative Affective Scale; STAI, State/Trait Anxiety Inventory; EPQ, Eysenck personality Questionnaire; ETB, Emotional Processing Test Battery; PILT, Probabilistic instrumental learning task; AVLT, Auditory verbal learning task.

Fig. 2.

The effect of a multispecies probiotic on the performance of emotion and cognitive measures after 28 days supplementation. (a) Accuracy at identifying facial expression of all emotions was significantly greater after probiotic intake (n = 26) than placebo (n = 25). Bar indicates the effect of the group (*p < 0.05). (b) Probiotic intake reduces attentional vigilance to positive and negative emotions in the dot-probe task. In the unmasked condition, there was a main effect of group (*p < 0.05) where probiotic supplemented subjects (n = 26) displayed less attention to happy and fearful emotions compared to placebo (n = 25). (c) The influence of the placebo or probiotic on the performance of the PILT after supplementation. There was an overall effect of group (*p < 0.05), where the good choice rate for both the win and loss trials were reduced by the probiotic (n = 26) compared to placebo (n = 25). (d) AVLT learning curves after placebo or probiotic supplementation. There was a significant group × trial interaction when comparing the recollection of List B words with List A/Trial 1 words. The recall of fewer List B words by the probiotic group was indicative of proactive interference. Probiotic intake did not affect List A recall (Trials 1–5), immediate recall (IR) or delayed recall (DR). *p < 0.05, group × List B/List A -Trial 1 interaction.

Fig. 3.

Salivary cortisol awakening response (CAR) and plasma CRP following placebo and probiotic supplementation. There were no significant differences in CAR, within and between probiotic (n = 35) and placebo (n = 36) groups at baseline (a) or after 28 days supplementation (b). No interactions or main effects of group on plasma CRP concentrations were observed following placebo (n = 26) or probiotic (n = 25) supplementation (c).