Tea and cardiovascular disease

Abstract

There is increasing evidence for a protective effect of tea consumption against cardiovascular disease. This review summarizes the available epidemiological data providing evidence for and against such an effect. We also review observational and intervention studies that investigated an effect of tea and tea extracts on cardiovascular risk factors, including blood pressure, serum lipids, diabetes mellitus, and obesity. Finally, we review potential mechanisms of benefit, including anti-inflammatory, anti-oxidant, and anti-proliferative effects, as well as favorable effects on endothelial function. Overall, the observational data suggest a benefit, but results are mixed and likely confounded by lifestyle and background dietary factors. The weight of evidence indicates favorable effects on risk factors and a number of plausible mechanisms have been elucidated in experimental and translational human studies. Despite the growing body evidence, it remains uncertain whether tea consumption should be recommended to the general population or to patients as a strategy to reduce cardiovascular risk.

Introduction

Tea leaves are obtained from the Camillia sinensis plant. Based on how the leaves are processed, three main types of tea can be produced: non-fermented green tea, partly fermented oolong tea and fermented black tea. Records from as far back as the 10th century BC indicate use of tea by man, largely because of its medicinal value. This review will focus on possible beneficial effects against cardiovascular disease.

Tea leaves contain a large amount of polyphenols (about 30% of the dry substance), mainly flavonoids. The major class of flavonoids in tea are flavanols, which include catechin, epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG) [1]. Total polyphenol content is similar in different types of tea, but the individual components vary, based in part on the degree of polyphenol oxidation during the manufacturing process. Catechins constitute about 80–90% and flavanols about 10% of the total flavonoids in green tea. On the other hand, theaflavins account for 50–60% and catechins only 20–30% of total flavonoids in black tea [2].

Recently, there has been considerable interest in the possibility that consumption of tea reduces risk for cardiovascular disease. Some observational studies suggest a benefit of tea, while other studies have failed to show such an association. Mechanistic studies have shown that tea and tea polyphenols have favorable effects on systemic risk factors and direct effects on the vasculature and platelets that might account for reduced cardiovascular risk. In the following sections, we will summarize the supportive and non-supportive observational studies that investigated a relationship between tea consumption and cardiovascular risk. We will then consider experimental, mechanistic and translational studies that elucidate potential mechanisms of benefit. Finally, we will attempt to put these data into clinical context given the considerable interest in dietary and lifestyle approaches to reduce cardiovascular disease.