If you haven’t been living in a cave, you’ve probably heard a little about the potential health benefits of green tea in regards to fat burning/weight loss, health, cancer, and antioxidant effects. This post is a review of a recent article from the American Family Physician – a Journal of the American Academy of Family Practice.
Green tea is derived from Camellia sinensis by lightly steaming and drying the leaves. Green tea, black tea, and oolong all come from the same plant but are prepared in different ways.
Green tea contains a variety of substances that are believed to provide the health benefits:
- Phenolic acids
The polyphenols appear to have antimutagenic, anti-diabetic, antibacterial, anti-inflammatory, and cholesterol lowering effects. The effects were demonstrated in vitro (in the lab) as well as in human and animal studies. Catechins comprise 60-80% of the polyphenols in green tea which is 20-45% polyphenols by weight. Because of the preparation of green tea, it contains higher amounts of catechins that oolong or black tea. Epigallocatechin gallate (EGCG) is the most studied and most prevalent catechin in green tea.
- Genital & perianal warts: Topical ointment of catechins for genital & perianal warts has been approved by the FDA. There is also possible use for an oral extract of sinecatechins for cervical lesions caused by HPV.
- Decreased risk of a variety of cancers with increased intake of green tea. Clinical trials are often poorly designed and with conflicting evidence. This is often due to a variety of population differences, dietary inconsistency, and environmental issues. A meta-analysis from 2006 showed a 20% reduction in breast cancer risk. Green tea reduced the stomach and esophageal cancer risk by about 50% in a Chinese study of over 18,000 men (odds ratio 0.52). Additionally, there is evidence that prostate cancer risk is reduced. Read the original article for more information.
- Weight loss: Green tea may also contribute to weight loss but the results of studies are conflicting. The details of these studies were not available in the article and the studies may not have been well designed. At least one study, which showed weight loss benefit, appeared to be fairly well done at first glance. More well designed studies are needed.
- Cardiovascular function: clinical studies are conflicted but epidemiological studies show a decreased risk of cardiovascular disease. At least one randomized, double-blinded, placebo controlled trial showed a decrease in LDL & total cholesterol. Again, more studies are needed.
Green tea is available as a tea (1 tsp leaves in 8 oz boiling water) or an extract.
Side Effects: most common is stomach upset & central nervous system simulation (due to caffeine content). At high doses, concentrated extracts have caused case reports of hepatotoxicity (liver issues). Green tea does contain a small amount of Vitamin K. One study showed coumadin (warfarin) antagonism at very high volumes (1/2-1 gallon) of green tea. There is also a possibility of folic acid antagonism at very high doses but no apparent evidence supporting this.
Bottom line: Green Tea appears to be safe and possibly effective for a number of conditions when consumed at normal doses.
References: The original article can be found here.