One study found that a short three week intervention with probiotics - containing milk drink
improved mood scores compared to participants who received a placebo.
Variability in mood was measured by the standard deviation of these
daily mood scores across each condition.
If you have seen it before, watch it again and pay attention to the absolutely
perfect mood score from Jerry Goldsmith.
As illustrated in Table 4, average happiness scores were negatively correlated with average sadness, anger, stress, and worry scores, and all
negative mood scores were positively correlated with each other.
The first formal investigation of a probiotic and human mental outlook involved 132 otherwise healthy adults consuming Lactobacillus casei fermented beverage for three weeks; vs. placebo, significant improvement
in mood scores were noted upon the among those with the higher baseline depressive symptoms [100].