Fruit polyphenols, immunity and inflammation

Flavonoids are a large class of naturally occurring compounds widely present in fruits, vegetables and beverages derived from plants. These molecules have been reported to possess a wide range of activities in the prevention of common diseases, including CHD, cancer, neurodegenerative diseases, gastrointestinal disorders and others. The effects appear to be related to the various biological/pharmacological activities of flavonoids. A large number of publications suggest immunomodulatory and anti-inflammatory properties of these compounds. However, almost all studies are in vitro studies with limited research on animal models and scarce data from human studies. The majority of in vitro research has been carried out with single flavonoids, generally aglycones, at rather supraphysiological concentrations. Few studies have investigated the anti-inflammatory effects of physiologically attainable flavonoid concentrations in healthy subjects, and more epidemiological studies and prospective randomised trials are still required. This review summarises evidence for the effects of fruit and tea flavonoids and their metabolites in inflammation and immunity. Mechanisms of effect are discussed, including those on enzyme function and regulation of gene and protein expression. Animal work is included, and evidence from epidemiological studies and human intervention trials is reviewed. Biological relevance and functional benefits of the reported effects, such as resistance to infection or exercise performance, are also discussed.