You may have heard the expression “knowledge is power.” Well – today – we’re going to give you more power to control your diet and lifestyle – by giving you the facts. Welcome to the Nutrition Facts podcast. I’m your host – Dr. Michael Greger.
Today we look at the surprising power – of green tea – one of the healthiest beverages we can drink. It has been associated with about a 30 percent reduction in breast cancer risk, and may protect against gynecological malignancies, such as ovarian cancer and endometrial cancer, as well as lower our cholesterol, blood sugar, and body fat.
In our first story we look at how green tea appears to work by boosting the immune system.
“The belief of green tea as a ‘wonder weapon’ against diseases dates back thousands of years.” I’ve talked about it in relation to chronic disease, but what about infectious disease? Interest in the antimicrobial activity of tea dates back to a military medical journal in 1906, suggesting that servicemen fill their canteens with tea to kill off the bugs that caused typhoid fever. However, this effect of tea was not studied further until the late 1980s, when tea compounds were pitted against viruses and bacteria in test tubes and petri dishes.
But what we care about is do they work in people? I had dismissed this entire field of inquiry as clinically irrelevant—until genital warts. “External genital warts,” caused by human wart viruses, “are one of the most common and fastest-spreading venereal diseases worldwide.”
“Patients with [external genital warts] present with one or several cauliflower-like growths on the genitals and/or anal regions,” considerably impairing people’s “emotional and sexual well-being.” But rub some green tea ointment on, and you can achieve “complete clearance of all warts” in more than 50% of cases.
Wow! If it works so well for wart viruses, what about flu viruses? Works great in a petri dish, but what about in people? Tea-drinking schoolchildren do seem to be protected. But you don’t know until it’s put to the test. If you give healthcare workers green tea compounds, they come down with the flu about three times less often than those given placebo. In fact, just gargling with green tea may help. While a similar effect was not found in high school students, gargling with green tea may drop the risk of influenza infection seven- or eight-fold, compared to gargling with water, in elderly nursing home residents, where flu can get really serious.
Unlike antiviral drugs, green tea appears to help by boosting the immune system, enhancing the proliferation and activity of gamma delta T cells, a type of immune cell that acts as “a first-line defense against infection.” “Subjects who drank six cups of tea per day had up to a 15-fold increase in [infection-fighting] interferon…production in as little as one week”—but why?
There’s actually a molecular pattern shared by cancer cells and pathogens and with “edible plant products, such as tea, apples, mushrooms, and wine.” And so, eating healthy foods may help maintain our immune cells on ready alert, effectively priming our gamma delta T cells “that then can provide natural resistance to microbial infections and perhaps tumors.”
I guess I shouldn’t have been so surprised—tea, after all, is “a vegetable infusion.” You’re basically drinking a hot water extraction of a dark green leafy vegetable.
Within 40 minutes of green tea consumption, we get a boost in antioxidant power in our bloodstream, and, within 60 minutes, an upregulation of DNA repair.
“[T]ea consumption is associated with a reduced risk of [heart disease], stroke,” and premature death in general, with each additional cup of green tea a day associated with a 4% lower mortality risk. So, maybe, “drinking several cups of tea daily can keep the doctor away”—as well as the mortician. But, what about cancer?
“There is growing evidence from laboratory, [population], and human intervention[al] studies that tea can exert beneficial disease-preventive effects,” and further, may actually “slow cancer progression.” Let’s review some of that evidence.
Not only do those who drink a lot of tea appear to live years longer than those who drink less, drinking lots of tea may delay the onset of cancer. The women that did get cancer appeared to get it seven years later if they had been drinking lots of tea compared to those who consumed less, whereas men had a three-year delay, the difference male versus female due, potentially, to smoking habits.
Green tea may be able to interfere with each of the stages of cancer formation: the initiation of the first cancer cell, promotion into a tumor, and then, the subsequent progression and spread. Cancer is often initiated when a free radical oxidizes our DNA, causing a mutation. But within 40 minutes of drinking green tea, you can get a nice “spike” in the antioxidant power of your bloodstream. “This increase…, in turn, [may] lower oxidative damage to DNA and so decrease [the] risk of cancer.”
Furthermore, in terms of “genoprotective effects”—protecting our genes—”pre-existing oxidation-induced DNA damage was…lower” after drinking green tea, suggesting that it can boost DNA repair as well. But, we didn’t know for sure, until now.
There’s a DNA-repair enzyme in our body called OGG1, and within one hour of drinking a single cup of green tea, we can boost its activity—though after a week of tea drinking, we can boost it even higher. So, “regular intake of green tea [may have] additional benefits in the prevention and/or repair of DNA damage.” Tea is so DNA-protective, it can be used for sperm storage for fresh samples until they can be properly refrigerated.
And so anti-inflammatory it can be used for pain control as a mouthwash after wisdom tooth surgery. And, in terms of controlling cancer growth, at a dose of green tea compounds that would make it into someone’s organs after drinking six cups of tea, it can cause cancer cells to commit suicide—apoptosis (programmed cell death)—while leaving normal cells alone.
There’s lots of chemo agents that can kill cancer through brute force. But that can make normal cells vulnerable too. So, “green tea appears to be potentially an ideal agent” for cancer prevention: “little or no adverse side effects,” efficacious for multiple cancers “at achievable dose levels,” and can be taken orally.
We have a sense of how it works: by stopping cancer cells from growing and causing them to off themselves. It’s cheap and has a history of safe, acceptable use. But this was all based on in vitro studies in a test tube. It needs to be evaluated in human trials: give people with cancer green tea to see if it helps.
Finally today, we examine the results of studies that use green tea to try to stop or reverse the progression of oral cancer, lung cancer, cervical cancer, and colon cancer.
Tea consumption may reduce the risk of getting oral cancer. Not only may the consumption of tea boost the antioxidant power of our bloodstream within minutes of consumption, and decrease the amount of free radical DNA damage throughout our systems over time, it can also increase the antioxidant power of our saliva, and decrease the DNA damage within the inner cheek cells of smokers—though not as much as stopping smoking altogether.
So, might this help precancerous oral lesions from turning into cancerous oral lesions? “More than [100,000] people develop oral cancer annually worldwide,” [with a] 5-year overall survival rate of less than” the flip of a coin. “Oral cancer frequently arises from” precancerous lesions in the mouth, with each have a few percent chance every year of turning cancerous. So, what a perfect opportunity to see if green tea can help.
“Fifty-nine…patients” with precancerous oral lesions were randomized into a tea group, in which capsules of powdered tea extract were given, as well as having the lesions painted with the green tea powder, versus a control group that essentially got sugar pills, and were painted with nothing. Within six months, lesions in 11 of the 29 in the tea group shrunk, compared to only 3 out of 30 in the placebo group. “The results indicate that tea treatment can improve the clinical manifestations of the oral lesions.”
The important question, though, is, did it prevent them from turning cancerous? But, because the trial only lasted a few months, they couldn’t tell. But, when they scraped some cells off of the lesions, there was a significant drop in DNA-damaged cells within three months in the treatment group—suggesting that things were going in the right direction. Ideally, though, we’d do a longer study, to see if they ended up with less cancer. And, while we’re at it, how about a study where they just used swallowed tea components, since most people don’t fingerpaint with tea in their mouths. We didn’t have such a study, though—until, we did.
Same extraordinary clinical results, with some precancerous lesions shrinking away. And, the study lasted long enough to see if fewer people actually got cancer. But, there was just as much new cancer in the green tea group as the placebo group. So, a higher response rate—I mean, the lesions looked better—but “no improvement in…cancer-free survival,” which is the whole point.
Now, these studies were done mostly on smokers and former smokers. What about lung cancer? Population studies suggest tea may be protective, but let’s put it to the test. Seventeen patients with advanced lung cancer given up to the equivalent of 30 cups of green tea a day, but “[n]o objective responses were seen.” Another study of 49 cancer patients—21 with lung cancer—who got between 4 and 25 cups worth of green tea compounds a day, and again, no benefits were found. The only benefit green tea may be able to offer lung cancer patients is to help lessen the burns from the radiation treatments when applied on the skin, as green tea compresses may be able to shorten the duration of the burns.
The protective effects of green tea applied topically were also seen in precancerous cervical lesions, where the twice-a-day direct application of a green tea ointment showed a beneficial response in nearly three-quarters of the patients, compared to only about a 10% response in the untreated control group, which is consistent with the anticancer effects of green tea compounds on cervical cancer cells in a petri dish. But, when women just got green tea extract pills to take, the pills didn’t seem to help.
I’ve talked about the potential benefit of green tea wraps for skin cancer. Is there any other cancer where green tea actually comes in direct contact? Yes, colon cancer, which grows from the inner surface of the colon that comes in contact with food and drink. In the colon, tea compounds are fermented by our good gut bacteria into compounds like 3,4DHPA, which appears to wipe out colon cancer cells, while leaving normal colon cells relatively intact in vitro.
So, 136 patients with a history of polyps were randomized to get green tea extract pills or not. Now, this was a study in Japan; so, everyone was already drinking green tea. So, effectively, this was comparing those who drank three cups a day to four cups a day. But, a year later on colonoscopy, the added green tea group had only half the polyp recurrence, and the polyps that did grow were 25% smaller. Why hasn’t a larger follow-up study been done since? Perhaps due to the difficulty in raising funds for the study, because green tea is a cheap beverage, not a pharmaceutical.
But the good news is that, thanks to a major cancer charity in Germany, researchers are currently recruiting for the largest green tea cancer trial to date, in which more than 2,000 patients will be randomized. That’s pretty it exciting.
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