Are the Tannins in Green Tea Unhealthy?

Most people think of green tea as being a healthy drink – and for good reason. People who choose green tea as their drink of choice may be reducing their risk of heart disease, cancer, dementia, stroke, diabetes, and even lowering their risk of obesity. Although more research is needed to confirm these positive effects, preliminary results look encouraging. What about the negative aspects of drinking green tea? One particular group of components, the tannins in green tea, have received some scrutiny. These astringent polyphenols give tea a bitter taste when present in high quantities. Are the tannins in green tea really healthy?

What Are Tannins?

Tannins are present not only in green tea leaves but in a variety of other plants and help to protect the plants against predators such as animals and insects. They’re also present in red wine and give it that tart taste that most wine manufacturers would like to avoid. They give unripe fruit their characteristic bitter taste, and are even found in beer and chocolate. As unappetizing as it may sound, tannins are also used to tan leather.

Are the Tannins in Green Tea Beneficial?

The tannins in green tea have anti-inflammatory, antibacterial, antiviral, and antiparasitic effects, and have even been shown to inhibit replication of the HIV virus. It’s hardly surprising that tannins would have these benefits since one of their primary functions is to protect plants against predators and disease. One way in which the tannins in green tea can be helpful to humans is by killing the bacteria that lead to gingivitis or gum disease. They may also help in the treatment of diarrhea and may reduce the risk of wound infection.

Do the Tannins in Green Tea Have Negative Effects?

One of the biggest problems associated with the tannins in green tea is their effect on iron absorption. Tannins form a complex with iron in the intestinal tract making it less readily absorbed and used by the body. For this reason, it’s recommended that green tea not be drank with meals to avoid interfering with iron absorption. Adding lemon to green tea can offset some of the effects of tannins on iron absorption. The tannins in green tea can also cause nausea and mild digestive upset in susceptible individuals. Tannins slow down protein digestion although large quantities would be needed for this to be a problem.

The Bottom Line?

The tannins in green tea have both positive and negative effects. The biggest concern is the effect they have on iron absorption. To offset this effect, drink green tea only between meals and add a few drops of lemon juice to each cup. This will help to increase absorption of iron as well as enhance the bioavailability of the catechins that make green tea such a healthy drink. If you have heart disease or high blood pressure, talk to your doctor before drinking caffeinated beverages such as green tea.

References:

http://www.lef.org/whatshot/2001_10.htm#tfgt

J. Nat. Prod. 53 (3): 587-95.