The beneficial effects of tea on immune function and inflammation: a review of evidence from in vitro, animal, and human research

Traditionally, tea has been drunk to eliminate toxins and to improve resistance to disease, although interest has mostly focused on cardiovascular disease risk reduction. This article therefore reviews evidence for the beneficial effects of tea flavonoids on immune function. The review focuses on key areas that include innate immunity and upper respiratory tract infections, gut health, oral health, and inflammatory processes. Important findings include the beneficial effects of tea extracts on fecal microflora balance, although the minimum effective dose requirements remain unclear. There is further evidence for the antimicrobial effects of tea in the upper respiratory tract and in inhibiting the growth of periodontal pathogens, although these effects have only been observed at high concentrations. Modulating effects of tea on the immune cells and markers of inflammation have been demonstrated, but robust data from human intervention trials are lacking. In summary, there is evidence to suggest that tea may have beneficial effects on certain immune parameters, which has implications for improving gut health and resistance against infections such as the common cold. However, further evidence from human studies, which control for potential confounding from lifestyle and biological factors, is required before strong conclusions can be made regarding the association between tea and immune function.