Michael Malone is with the Department of Family and Community Medicine at the Penn State College of Medicine in Hershey, Pennsylvania. Gary Tsai is with Torrance Memorial Physician Network in California.
The authors reported no potential conflict of interest relevant to this article, which originally appeared in The Journal of Family Practice (2018;67[1]:10-16).
Most tea leaves come from the Camellia sinensis bush, but green and black tea are processed differently to produce different end products.23 It is estimated that green tea accounts for approximately a quarter of all tea consumption and is most commonly consumed in Asian countries.23 The health-promoting effects of green tea are mainly attributed to its polyphenol content.24 Of the many types of tea, green tea has the highest concentration of polyphenols, including catechins, which are powerful antioxidants.23,24 Green tea has been used in traditional Chinese and Indian medicine to control bleeding, improve digestion, and promote overall health.23
Dementia. Green tea polyphenols may enhance cognition and may protect against the development of dementia. In-vitro studies have shown that green tea reduces hydrogen peroxide and ß-amyloid peptides, which are significant in the development of Alzheimer’s disease.25 A 12-subject double-blind study found green tea increased working memory and had an impact on frontoparietal brain connections.26 Furthermore, a cohort study with 13,645 Japanese participants over a five-year period found that frequent green tea consumption (> 5 cups per day) was associated with a lower risk for dementia.27 Additional studies are needed, but green tea may be useful in the treatment or prevention of dementia in the future.
Coronary artery disease. In one study, greentea plasma and urinary concentrations were associated with plasma biomarkers of cardiovascular disease and diabetes.28In one review, the consumption of green tea was associated with a statistically significant reduction in LDL cholesterol.29 Furthermore, a 2015 systematic review and meta-analysis of prospective observational studies concluded that increased tea consumption (of any type) is associated with a reduced risk for coronary heart disease, cardiac death, stroke, and total mortality.30
Cancer. Many studies have shown that green tea may reduce the risk for cancer, although epidemiologic evidence is inconsistent. Studies have shown that cancer rates tend to be lower in those who consume higher levels of green tea.31,32 Whether this can be attributed solely to green tea remains debatable. Several other studies have shown that polyphenols in green tea can inhibit the growth of cancer cells, but the exact mechanism by which tea interacts with cancerous cells is unknown.23
Several population-based studies have been performed, mostly in Japan, which showed green tea consumption reduced the risk for cancer. Fewer prostate cancer cases have been reported in men who consume green tea.33 While studies have been performed to determine whether green tea has effects on pancreatic, esophageal, ovarian, breast, bladder, and colorectal cancer, the evidence remains inadequate.32
Diabetes. Green tea has been shown in several studies to have a beneficial effect on diabetes. A retrospective Japanese cohort study showed that those who consumed green tea were one-third less likely to develop type 2 diabetes.34 A 10-year study from Taiwan found lower body fat and smaller waist circumference in those who consumed green tea regularly.35 A 2014 meta-analysis and systematic review of tea (any type) consumption and the risk for diabetes concluded that three or more cups of tea per day was associated with a lower risk for diabetes.36 Another meta-analysis of 17 RCTs focused on green tea concluded that green tea improves glucose control and A1C values.37
