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.
Highlights
Our island, “Okinawa”, is in the southernmost prefecture of Japan called Okinawa, which is composed of 160 islands scattered over a vast area of about 400 km north to south and 1000 km east to west
It has been suggested that flavonoids reduce the incidence of upper respiratory tract infections (URTIs) because they have a range of physiological effects in humans, including antiviral and anti-inflammatory effects [7]
We found that immunoglobulin A (IgA) (688.68 ± 85.50 and 512.11 ± 66.4 vs. 279 ± 67.97 mg/dL; p < 0.01and p < 0.05) (Figure 3A) and immunoglobulin G (IgG)
Summary
“Okinawa”, is in the southernmost prefecture of Japan called Okinawa, which is composed of 160 islands scattered over a vast area of about 400 km north to south and 1000 km east to west. People have been eating a group of locally grown plants, called island vegetables, since ancient times. Our island is a crescent-shaped archipelago, and the natural forests hold a huge variety of unique subtropical plants with relatively high endemism [2]. The plants are known to produce phytochemicals [3]. The antioxidant activity of the phytochemicals in Okinawan vegetables, which grow under exposure to ultraviolet light stronger than that in other prefectures in our country, is high [4]. The dietary flavonoids, especially their glycosides, are the most vital phytochemicals in the diet and are of great general interest due to their diverse bioactivity. Increasing scientific evidence has shown that flavonoids that are found in fruits and vegetables can have antiinflammatory properties [6].
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