ABSTRACT
BACKGROUND: It has been hypothesized that flavonoid ingestion stimulates immunity, promotes health, and prevents human illness. The aim of this analysis was to evaluate the association of the levels of immunoglobulin A (IgA) with the prevention of influenza infections and with the polyphenols contained in Okinawan vegetables. METHODS: IgA, immunoglobulin G (IgG), immunoglobulin M (IgM), and soluble interleukin-2 receptor (sIL-2R) levels were measured in 44 outpatients who regularly ingested vegetables grown on Okinawa Island (200-300 g/day for ≥ 300 days/year) with no history of influenza infection and in 73 patients who ingested the vegetables irregularly or not at all with a history of influenza infection. RESULTS: The patients who regularly ate Okinawan vegetables had higher IgA, IgG, and IgM levels than those who did not. On the other hand, patients who did not consume Okinawan vegetables and had influenza had lower IgA, IgG, and IgM levels. In addition, the IgA and IgG levels showed significant positive correlations with the sIL-2R levels in both groups. CONCLUSIONS: It may be beneficial to eat vegetables abundant in polyphenols every day. Secretory IgA antibodies are an important part of the immune defense against viral diseases. People who ingest Okinawan vegetables have high IgA levels and might be more likely to develop immunity against influenza RNA viruses.