REVIEW QUESTION

Is green tea beneficial in the prevention of cancer?

TYPE OF REVIEW

A systematic review of 142 studies from 10 countries, with over 1.1 million participants.

RELEVANCE FOR NURSING

Green tea, a traditional component of the Asian diet, is now consumed all over the world for alleged health benefits such as reduction in the risk of chronic disease and weight loss. A potential benefit of green tea consumption is the prevention of cancer, cardiovascular diseases, diabetes, and inflammation. The polyphenols found in green tea, which are thought to act as antioxidants, may also have a protective effect on Alzheimer's disease, although studies are inconclusive.

However, the benefits of green tea should be weighed against its potential harms, such as reported hepatotoxicity from its use as a dietary supplement for weight loss. In addition, green tea catechins are known to disrupt iron absorption, potentially causing iron deficiency anemia if the tea is consumed in substantial quantities.

CHARACTERISTICS OF THE EVIDENCE

This review sought to identify associations between green tea consumption and the development of cancer (including prostate, gynecologic, and nonmelanoma skin cancer) and cancer death. It included 11 experimental and 131 nonexperimental studies from 10 countries. The majority of participants were from Asian populations and all were over the age of 18 years. Participants consumed green tea as either a tea to drink or an extract taken orally in powder, tablet, or liquid form. Studies included experimental research (such as randomized controlled trials comparing green tea extract with placebo) or nonexperimental research (such as cohort and case-control observational studies).

In the 11 experimental studies, all 1,795 participants consumed green tea extract or placebo and all results were derived from low-certainty evidence. Green tea consumption modestly increased the incidence of gynecologic cancer in the two studies reporting on this cancer. One study assessing nonmelanoma skin cancer showed no benefit from the consumption of green tea extract. The results for prostate cancer were drawn from three studies with 201 total participants and indicated a reduced risk of prostate cancer with green tea consumption; however, all participants were at high risk for prostate cancer when recruited into the studies.

In the nonexperimental studies, which comprised 46 cohort and 85 case-control studies and over 1.1 million participants, after comparing the highest with the lowest green tea intake, there was a lower overall cancer incidence and no association between green tea consumption and cancer mortality. The certainty of the evidence was of low quality, making it difficult for health professionals to draw conclusions.

BEST PRACTICE RECOMMENDATIONS

Based on the studies in this review, evidence to support the benefits of green tea in reducing cancer risk is inconclusive. There is some indication, from the randomized controlled trials and case-control studies, of a beneficial effect for particular site cancers, such as urogenital tract cancer. Most studies were conducted in Asian countries, presenting a population bias. For this reason, extrapolating findings to other populations must be done with caution.

In assessing patients for anemia, nurses should ask about their tea intake. There is evidence that tea interferes with iron absorption, potentially causing anemia. Based on the results of this review, nurses need to ensure that aspects of self-care, such as green tea consumption, are disclosed in assessment conversations and documented in self-care planning.

SOURCE DOCUMENT