This single-center, randomized, double-blind and controlled study aims to examine the effect of a fermented dairy product containing the probiotic Lactobacillus casei DN-114 001 (Actimel® = tested product) on the incidence of respiratory and gastro-intestinal common infectious diseases (cumulated number of infections during the intervention period: primary criteria), and on immune functions in healthy shift workers. Volunteers received either 200g/day of tested product (N=500) or control product (N=500) for 3-months, followed by a 1-month follow-up.

Inclusion criteria: male and female aged 18-65 years; working in 2- or 3-shift work patterns (including night work); same job position for at least 4.5 months; a 19 to 30 kg/m2 body mass index; no symptoms of CIDs during the 2 weeks before product consumption; agreeing to a written informed consent.

Exclusion criteria: part time work (<90%); allergy/hypersensitivity to components of the study product; severe respiratory allergy; a situation which, in the investigator's opinion, could interfere with optimal participation or constitute a special risk for the volunteer; a history of chronic metabolic/gastro-intestinal disease (except appendectomy); surgery/intervention requiring general anesthesia in the last 4 weeks; administration of systemic/topical treatments likely to interfere with the evaluation parameters in the last 4 weeks; chronic disease requiring antibiotics/antiseptics/anti-inflammatory medications; special medicated diet; chronic/iatrogenic immunodeficiency; cardiac/renal/respiratory insufficiency; severe evolutive/chronic pathology; pregnancy, breast feeding or lacking effective contraception in females; susceptibility not to comply with dietary recommendation during the study period.