More Evidence of Green Tea’s Effectiveness Is Needed

Letter to the editor: In this article’s Strength of Recommendations Taxonomy (SORT) table, three of the recommendations said “results are mixed,” “studies are inconsistent,” or “the evidence is conflicting.” When conflicting results are found in small controlled studies and epidemiologic studies, the most likely explanation is that there is no real effect. Ioannidis has shown why most published research findings are false.1 Research methodologist Bausell shows in his book Snake Oil Science: The Truth About Complementary and Alternative Medicine that many factors conspire to produce false-positive results, particularly in studies of alternative medicine.2

A rigorously scientific analysis of all the green tea research can be best interpreted as telling us there is no good evidence to support its use for conditions such as cancer, weight loss, or cardiovascular disease. The Natural Medicines Comprehensive Database, a resource for evidence-based, clinical information on natural medicines, rates green tea as only “possibly effective.” This rating is below their ratings of “effective” and “probably effective.”3 It raises a number of concerns about safety and interactions with other drugs, laboratory tests, and diseases. Additional concerns are that the dosage from brewed tea is variable, and commercial green tea extracts are classified as “diet supplements” under the Diet Supplement Health and Education Act and are not regulated for safety, purity, and content. Contamination and inconsistency of such products is common. In my opinion, we should not recommend green tea to our patients unless more convincing evidence is found.

Originally published as a Letter to the Editor in American Family Physician. https://www.aafp.org/afp/2010/0701/p17.html 

Dr. Hall is a contributing editor to both Skeptic magazine and the Skeptical Inquirer. She is a weekly contributor to the Science-Based Medicine Blog and is one of its editors. She has also contributed to Quackwatch and to a number of other respected journals and publications. She is the author of Women Aren’t Supposed to Fly: The Memoirs of a Female Flight Surgeon and co-author of the textbook, Consumer Health: A Guide to Intelligent Decisions.