Should You Consider Green Tea to Lower Your Cancer Risk?

Green tea is native to China and India and has been consumed for centuries throughout the world. It is chock full of antioxidants and other substances and may be one of the planet's healthiest beverages. I recently came across an article lauding the anti-cancer properties of green tea. Today I want to explore with you whether or not there is evidence that green tea consumption lowers cancer risk.

We begin with breast cancer. One comprehensive review included 5,617 enrolled in two studies of breast cancer recurrence and seven studies of breast cancer incidence. Those who consumed the most tea had a drop of up to nearly one-third in the risk of getting breast cancer. Promising, but not high-level evidence, given the observational nature of the study.

What about other cancers? A comprehensive review of 29 studies discovered that those who consumed green tea had a 42 percent lower risk of developing colorectal cancer. However, the benefit seemed to accrue only to patients with rectal cancer and to females.

A separate population-based prospective study found regular consumption of green tea to be inversely associated with colorectal cancer risk, particularly among women who maintained the tea-drinking habit over time.

The longer the duration of tea consumption over one’s life, the lower the risk of colorectal cancer appears to be. Risk also drops as the amount of tea consumed rises. The investigators conducted the research prospectively and tried to adjust for a wide range of confounding factors (including socioeconomic status). This Shanghai study of women consumers of green tea represents some of the best evidence I could find.

That’s the good news. The bad? An observational study cannot measure tea intake amount with any degree of high confidence. Therefore, the study does not represent high-level evidence.

What about prostate cancer? One study from China hinted that large amounts of green tea are associated with a lower risk of prostate cancer. Of those without prostate cancer, 80 percent consumed tea. Among those with prostate cancer, only 55 percent drank the beverage. The prostate cancer risk dropped with increasing frequency, duration, and quantity of green tea consumption.

On the other hand, while a 2007 Japanese study found no reduction between green tea consumption and the risk of localized prostate cancer, there appeared to be a reduction in finding advanced disease. For men consuming five or more cups per day (compared to less than one cup daily), the risk of advanced prostate cancer dropped by half.

So should you drink green tea if you want to reduce your risk of prostate cancer? Not so fast. Other studies, including one looking at nearly 20,000 Japanese men, have not found a risk-reduction.

I do not think we have any high-level evidence to assert an association between green tea consumption and a reduction in overall cancer risk. I believe that we have hints of a protective effect, particularly as there is some dose-response data. I would love to see a prospective, randomized trial to answer the question, but such dietary studies are notoriously challenging to complete.

Now, the caveats. Green tea may interact with conventional cancer treatments. Enzymes in green tea may also metabolize other types of chemotherapy. This can increase the levels of certain chemotherapy drugs.

The Food and Drug Administration (FDA) offers that “there is no evidence to support health claims for green tea consumption and a lower risk of stomach, lung, colorectal, esophageal, pancreatic, ovarian, and combined cancers.”

Finally, an 8-ounce (230 milliliters) cup of green tea has about 30 to 50 milligrams of caffeine. The recommended maximum caffeine per day is 400 milligrams, the equivalent of approximately eight cups of green tea. Of course, it would not be prudent to consume all eight cups at once (especially if you are similar to me and sensitive to caffeine)!

The bottom line? Green tea is tasty (to some) and may have some health benefits. Whether it reduces the risk of cancer remains unclear.