Background: A suppressed immune response has been documented in students under examination stress.

Aims: The current study aimed to evaluate the effect of milk fermented with yogurt cultures plus Lactobacillus casei DN-114001 (Actimel) 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 100mL 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 microg/dL in the control group, and 1.75+/-1.05 microg/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.