The effect of milk fermented by yogurt cultures plus Lactobacillus casei DN-114001 on the immune response of subjects under academic examination stress

Background A suppressed immune response has been documented in students under examination stress. Aim of the study The current study aimed to evaluate the effect of milk fermented with yogurt cultures plus Lactobacillus casei DN-114001 (Actimel(R)) on the immune system of subjects under academic examination stress. Methods University students were allocated to one of two groups, receiving during 6 weeks ( 3 weeks prior to, as well as the 3-week duration of the examination period) either: a) a glass of semi-skimmed milk each day ( control group, n = 63) or b) two 100 mL portions per day of fermented milk ( treatment group, n = 73). Anxiety and immunological measurements were monitored at baseline ( Phase 0) and study end ( Phase 1). Results The results were expressed as the differences between the data obtained from Phase 0 and Phase 1. This was calculated by subtracting Phase 1 results from the Phase 0 and it is denominated Treatment effect. Mean ( +/- SE) anxiety increased significantly (P< 0.05) over the 6-week study in all students, from 40.74 +/- 2.50 to 61.19 +/- 2.64 (in percentiles). There was no significant treatment effect since this increase was similar in the control and the treatment groups (21.65 +/- 5.09 vs 19.14 +/- 3.67, respectively). However, there was a significant treatment effect ( P< 0.05) on the mean change in absolute number of lymphocytes during the 6-week study, which decreased in the control group ( - 0.04 +/- 0.12 cells x 10(3)/mm(3)) and increased in the treatment group (0.37 +/- 0.11 cells x 10(3)/mm(3)). There was also a significant treatment effect (P< 0.05) on the change in absolute numbers of CD56 cells during the 6-week study. Mean absolute CD56 cells significantly decreased ( P< 0.05) in the control group ( - 51.97 +/- 21.33 cells/mm(3)), while remaining similar in the treatment group (17.29 +/- 17.27 cells/mm(3)). During the study, mean serum cortisol increased 4.30 +/- 0.98 mug/dL in the control group, and 1.75 +/- 1.05 mug/dL in the treatment group and no significant differences were found between both values (P = 0.062). Conclusions Milk fermented with yogurt cultures plus Lactobacillus casei DN-114001 was able to modulate the number of lymphocytes and CD56 cells in subjects under academic examination stress.