Improving Effect of Acetic Acid Bacteria (<i>Gluconacetobacter hansenii</i> GK-1) on sIgA and Physical Conditions in Healthy People: Double-Blinded Placebo-Controlled Study

It is known that the consumption of bacteria such as lactobacilli and bifidobacteria has beneficial effects on human immune function. Most of them are Gram-positive bacteria, and there are few reports on Gram-negative bacteria. In this study, we evaluated the effects of intake of Gluconacetobacter hansenii GK-1 (GK-1), Gram-negative acetic acid bacteria, for 12 weeks on physical condition and immune indices. We conducted a randomized, double-blind, placebo-controlled, parallel-group study in 100 healthy adults. The subjects were randomized into the GK-1 and the placebo groups. The diary-administered physical condition survey was conducted during the study period. The evaluation of salivary sIgA levels, NK-cell activity, and serum IFN-γ levels and quality of life survey was conducted before, in 6 weeks, and 12 weeks after the start of ingestion. Based on the physical condition survey, the cumulative onset-days of symptoms were significantly suppressed in the GK-1 group compared to the placebo group regarding the evaluation of 13 symptoms related to immunity, every 3 weeks. Additionally, salivary sIgA levels per hour were significantly increased in the GK-1 group compared with the placebo group at 6 and 12 weeks. Despite no significant differences in the NK-cell activity, serum IFN-γ levels or quality of life survey between the groups. Serum IFN-γ levels in the GK-1 group were significantly elevated at 12 weeks after the start of ingestion compared with those before ingestion. In conclusion, intake of GK-1 was shown to increase salivary sIgA levels and improve physical condition. This suggested that oral intake of GK-1 may help maintain the immune system.