Drinking Tea: Are the Health Benefits Real?

Therapeutic Effects of Tea

The potential health benefits of tea consumption have been the subject of thousands of studies, many of which have examined the role of polyphenols (eg, epigallocatechin gallate in green tea, theaflavins and thearubigins in black tea). Polyphenols (including flavonoids) are a class of phytochemicals believed to give tea (as well as coffee, certain vegetables, fruits, and grains) its antioxidative properties, flavor, color, and smell. These strong antioxidants may reduce the oxidation of low-density lipoprotein (LDL) cholesterol and lower the risk for heart disease. They may also have anticarcinogenic effects stemming from their potential to mediate the oxidation of DNA and by inducing glucuronosyltransferases, thereby helping to eliminate toxicants and carcinogens.^[9] Tea polyphenols may also promote favorable intestinal bacterial flora and inhibit reactive oxygen species associated with age-related diseases.^[9]

Potential Benefits

Currently, some of the most promising avenues for research on tea consumption are related to the positive effects of flavonoids on coronary artery disease and stroke.^[10] Total intake of flavonoids and flavones is associated with lower risks for fatal cardiovascular disease.

Grassi and colleagues^[11] evaluated how flavonoids found in tea may affect flow-mediated dilation and help counter endothelial dysfunction, an early phase in the pathogenesis of atherosclerosis. Although these effects are not completely understood, current evidence suggests that moderate tea drinking may enhance endothelium-dependent vasodilation and help explain the positive benefits of tea on cardiovascular health.

In lab animals, tea has been shown to protect against lead- and cadmium-induced oxidative stress,^[12] which appears to support the hypothesis that tea may increase the body's oxidative capacities. Another study^[13] examined the effects of tea polyphenols on oxidative stress, and whether the circadian clock could explain the protective effect. Tea polyphenols were shown to ameliorate redox imbalance and mitochondrial dysfunction in hepatocytes.^[13]

Ide and colleagues^[14] reviewed several well-conducted studies that support the promising antioxidative and anti-inflammatory effects of tea catechins on oxidative stress, considered a key component of the pathologic mechanism underlying Alzheimer disease.

Potential Harms

In a large population-based case-control study, Yang and colleagues^[15] concluded that drinking very hot tea significantly increased the risk for esophageal squamous cell carcinoma in a sample of high-risk Chinese men, especially in those who also consume alcohol. In a related editorial, Cronin-Fenton^[16] posited that it is plausible that the observed increased esophageal cancer risk is attributable to thermal injury caused by drinking very hot tea rather than to the tea per se, and encourages tea drinkers to allow their tea to cool before consuming. The International Agency for Research on Cancer's view is that consuming hot beverages of any type is "probably carcinogenic."^[17]

Caffeine exposure from tea. All types of tea derived from the C sinensis plant contain caffeine; however, various factors (eg, tea leaf processing, tea type, brew method, and strength) affect the amount of caffeine in tea. The most widely reported estimates reveal that the lowest amount of caffeine (per 8 oz) is found in the yellow and white teas (30-55 mg) followed by green (35-70 mg), oolong (50-75 mg), and black teas (60-90 mg). The same size cup of coffee contains about 100 mg caffeine. No recent studies have focused on the harms of caffeine exposure from tea per se; rather, concerns about the safety of caffeine to date seem to be tied primarily to the dose of caffeine, regardless of source.^[18]

Medscape © 2019 WebMD, LLC

Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.

Cite this: Drinking Tea: Are the Health Benefits Real? - Medscape - Jan 17, 2019.