The Role of Tea in Human Health: An Update

Abstract

Tea is an important dietary source of flavanols and flavonols. In vitro and animal studies provide strong evidence that tea polyphenols may possess the bioactivity to affect the pathogenesis of several chronic diseases, especially cardiovascular disease and cancer. However, the results from epidemiological and clinical studies of the relationship between tea and health are mixed. International correlations do not support this relationship although several, better controlled case-referent and cohort studies suggest an association with a moderate reduction in the risk of chronic disease. Conflicting results between human studies may arise, in part, from confounding by socioeconomic and lifestyle factors as well as by inadequate methodology to define tea preparation and intake. Clinical trials employing putative intermediary indicators of disease, particularly biomarkers of oxidative stress status, suggest tea polyphenols could play a role in the pathogenesis of cancer and heart disease.

• tea
• flavonoids
• cardiovascular disease
• cancer
• bone health
• oral health
• thermogenesis
• iron status
• cognitive function
• kidney stones

Key teaching points:

• Tea is a rich source of polyphenolic flavonoids which exhibit potent antioxidant activity in vitro and in vivo. The flavonoid content of tea depends upon the type of tea and preparation method.

• Contrasting results have arisen from human studies of the relationship between tea and health, particularly the risk for cardiovascular disease and cancer. A limited number of studies suggest a beneficial impact of tea intake on bone density, cognitive function, dental caries and kidney stones.

• Randomized clinical trials examining the effect of tea on putative intermediary biomarkers, e.g., homocysteine for heart disease and 8-hydroxy-2′-deoxyguanosine for cancer, and physiological responses like brachial artery dilation suggest a potential health benefit from tea consumption.

• Human studies examining the effects of tea on health must carefully define tea preparation and intake (including amount, frequency and timing) and control or adjust for confounding by socioeconomic and lifestyle factors.

Key teaching points:

• Tea is a rich source of polyphenolic flavonoids which exhibit potent antioxidant activity in vitro and in vivo. The flavonoid content of tea depends upon the type of tea and preparation method.

• Contrasting results have arisen from human studies of the relationship between tea and health, particularly the risk for cardiovascular disease and cancer. A limited number of studies suggest a beneficial impact of tea intake on bone density, cognitive function, dental caries and kidney stones.

• Randomized clinical trials examining the effect of tea on putative intermediary biomarkers, e.g., homocysteine for heart disease and 8-hydroxy-2′-deoxyguanosine for cancer, and physiological responses like brachial artery dilation suggest a potential health benefit from tea consumption.

• Human studies examining the effects of tea on health must carefully define tea preparation and intake (including amount, frequency and timing) and control or adjust for confounding by socioeconomic and lifestyle factors.

Supported in part by the U.S. Department of Agriculture (USDA) Agricultural Research Service under Cooperative Agreement No. 581950-9-001 and the Tea Council of the USA. The contents of this publication do not necessarily reflect the views or policies of the USDA nor does mention of trade names, commercial products or organizations imply endorsement by the U.S. government.

Notes

Disclosures: Dr. Blumberg is a member of the Scientific Advisory Panel of the Tea Council of the USA. An honorarium was provided in partial support for this manuscript by the Tea Council of the USA.