There are a number of studies that show probiotic supplementation to be beneficial to the immune system. Research appearing in the journal, Vaccine (Volume 24, Issues 44-46, 10 November 2006, Pages 6670-6674) looked at probiotic supplementation and its effect on upper respiratory tract infections (colds and the flu). The double-blind, placebo-controlled study took place during two winter/spring periods. The subjects were 479 healthy adults who were supplemented with a vitamin/mineral supplement containing probiotics (lactobacilli and bifidobacteria) or a placebo that contained only the vitamin/mineral supplement. Taking the probiotic did not reduce the number of upper respiratory infections, but they did significantly shorten the duration of the illness (by nearly two days, compared to the placebo group). Also, the symptoms were less severe in the probiotic group. Taking the probiotics also increased the number of immune cells (cytotoxic T plus T suppressor cell counts and in T helper cell counts).
Another study appearing in the International Journal of Sports Nutrition, Exercise and Metabolism (2011 Feb; 21(1): 55-64) looked at the use of probiotics and their effect on the immune systems of 58 athletes. The 58 subjects of the study were randomly assigned to receive either a probiotic supplement (Lactobacillus casei Shirota) for a period of 16 weeks. The placebo group had 36% higher incidence of upper respiratory infections (URTI) compared to the group receiving the supplement. According to the authors, “Regular ingestion of LcS appears to be beneficial in reducing the frequency of URTI in an athletic cohort, which may be related to better maintenance of saliva IgA levels during a winter period of training and competition.”
The second surprising thing that helps the immune system is green tea. It turns out that drinking green tea may also reduce the chances of coming down with the flu. The researchers looked at questionnaires about green tea consumption taken twice during flu season. Drinking between one and five cups of green tea per day reduced the incidence of influenza. Researchers found that there was a This relation between tea consumption and the incidence of influenza (confirmed by antigen testing) was published in the Journal of Nutrition (201 Oct; 141(10): 1862-1870).