Elevation of natural killer cell activity and alleviation of mental stress by the consumption of yogurt containing Lactobacillus gasseri SBT2055 and Bifidobacterium longum SBT2928 in a double-blind, placebo-controlled clinical trial

We conducted a placebo-controlled, randomized, double-blind clinical trial using a yogurt containing two different probiotics to test their immunomodulatory and stress-related functions. The subjects were divided into two groups (109 placebo subjects and 115 test subjects). The test yogurt contained two probiotics, Lactobacillus gasseri SBT2055 and Bifidobacterium longum SBT2928, in a starter yogurt. Before and after the consumption of either the test or placebo yogurt for 12 weeks (100 g/day), we measured the participants' natural killer (NK) cell activities and the levels of two stress-induced hormones, adrenocorticotrophic hormone (ACTH) and cortisol. We found that the NK cell activities of the test yogurt group were higher than those of the placebo yogurt group, and most intriguingly, their serum ACTH levels were significantly decreased by the test yogurt. These results suggest that the probiotic-containing test yogurt confers health benefits not only by enhancing innate immunity but also by alleviating stress.