Boosting Antiviral Immune Function with Green Tea

Unlike most antiviral drugs, green tea appears to work by boosting the immune system to combat diseases such as genital warts (caused by HPV) and the flu (caused by the influenza virus).

According to one study, “The belief in 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? I explore this in my video Benefits of Green Tea for Boosting Antiviral Immune Function. Interest in the antimicrobial activity of tea dates back to a military medical journal in 1906, which suggested 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 whether it works in people. I had dismissed this entire field of inquiry as clinically irrelevant until I learned about tea’s affect on 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…associated with…considerable impairment of patients’ emotional and sexual well-being.” But rub on some green tea ointment, and you can achieve complete clearance of all warts in more than 50 percent of cases.

If it works so well for wart viruses, what about flu viruses? As you can see at 1:41 in my video, it works great in a petri dish, but what about in people? Well, tea-drinking school children seem to be protected, but you don’t know about the broader population 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, as you can see at 2:02 in my video. 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 residents of a nursing home, where flu can get really serious.

Unlike antiviral drugs, green tea appears to work 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.” According to the researchers, “Subjects who drank six cups of tea per day had up to a 15-fold increase in [infection-fighting] interferon gamma production in as little as one week”—but why?

There is in fact a molecular pattern shared by cancer cells, pathogens, and “edible plant products such as tea, apples, mushrooms, and wine.” So, eating healthy foods may help maintain our immune cells on ready alert, effectively priming our gamma delta T cells so they “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.

For more on what green tea can (and cannot) do, check out videos such as:

How else can we improve our immune function? See, for example:

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:


Using Green Tea to Help Prevent Cancer and Treat Cancer

Tea 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-percent lower mortality risk. So, perhaps “drinking several cups of tea daily can keep the doctor away,” as well as the mortician—but what about cancer?

As I discuss in my video Can Green Tea Help Prevent Cancer, there is “growing evidence from laboratory, epidemiologic [population], and human intervention 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 longer than those who drink less, as you can see at 0:49 in my video, drinking lots of tea may also delay the onset of cancer. At 0:56 in my video, you can see a table titled “Average age at cancer onset and daily green tea consumption.” The green tea intake is measured in Japanese tea cups, which only contain a half a cup, so the highest category in the table is actually greater than or equal to five full cups of tea, not ten as it appears in the table. Women who did get cancer appeared to get it seven years later if they had been drinking lots of tea compared to those who had consumed less. Men, however, had a three-year delay in cancer onset if they had consumed more than five full cups of green tea daily, the difference potentially “due to higher tobacco consumption by males.”

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 subsequent progression and spread, as you can see at 1:24 in my video. Cancer is often initiated when a free radical oxidizes our DNA, causing a mutation, but, as you can see at 1:44 in my video, we can get a nice “spike of antioxidant power” of our bloodstream within 40 minutes of drinking green tea. “This increase may, in turn, lower oxidative damage to DNA and so decrease risk of cancer.”

Furthermore, in terms of genoprotective effects—that is, protecting our genes—pre-existing oxidation-induced DNA damage was lower after drinking green tea, suggesting consumption can boost DNA repair as well. We didn’t know for certain, however…until now.

There is a DNA-repair enzyme in our body called OGG1. As you can see at 2:15 in my video, within one hour of drinking a single cup of green tea, we can boost OGG1’s activity, and after a week of tea drinking, we can boost it even higher. So, “regular intake of green tea has additional benefits in the prevention and/or repair of DNA damage.” In fact, tea is so DNA-protective it can be used for sperm storage for fresh samples until they can be properly refrigerated.

What’s more, tea is so anti-inflammatory it can be used for pain control as a mouthwash after wisdom tooth surgery, as you can see at 2:41 in my video. In terms of controlling cancer growth, at a dose of green tea compounds that would make it into our 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 are a number of chemotherapy agents that can kill cancer through brute force, but that can make normal cells vulnerable, too. So, “[g]reen 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 able to be taken orally. We have a sense of how it works—how it stops cancer cells from growing and causing them to kill off themselves—and it’s cheap and has a history of safe, acceptable use. But, all of this was based on in-vitro studies in a test tube. “It needs to be evaluated in human trials,” concluded the researchers. Indeed, what happens when we give green tea to people with cancer? Does it help?

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 and decrease the amount of free-radical DNA damage throughout our systems over time, but 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 all together. You can see several graphs and tables showing these findings in the first 35 seconds of my video Can Green Tea Help Treat Cancer?.

Might this help precancerous oral lesions from turning into cancerous oral lesions? More than 100,000 people develop oral cancer annually worldwide, with a five-year overall survival rate of less than the flip of a coin. Oral cancer frequently arises from precancerous lesions in the mouth, each having a few percent chance of turning cancerous every year. Can green tea help?

Fifty-nine patients with precancerous oral lesions were randomized into either a tea group, in which capsules of powdered tea extract were given and their lesions were painted with green tea powder, or a control group, who essentially got sugar pills and their lesions painted with nothing but glycerin. As you can see at 1:23 in my video, within six months, lesions in 11 out of the 29 in the tea group shrunk, compared to only 3 of 30 in the placebo group. “The results indicate that tea treatment can improve the clinical manifestations of the oral lesions.”

The most important question, though, is whether the tea treatment prevented the lesions from turning cancerous. Because the trial only lasted a few months, the researchers couldn’t tell. When they scraped some cells off of the lesions, however, there was a significant drop in DNA-damaged cells within three months in the treatment groups, suggesting that things were going in the right direction, as you can see at 1:46 in my video. Ideally, we’d have a longer study to see if they ended up with less cancer and one that just used swallowed tea components, since most people don’t finger-paint with tea in their mouths. And, we got just that.

As you can see at 2:15 in my video, there were the same extraordinary clinical results with some precancerous lesions shrinking away. What’s more, the study lasted long enough to see if fewer people actually got cancer. The answer? There was just as much new cancer in the green tea group as the placebo group. So, the tea treatment resulted in a higher response rate, as the lesions looked better, but there was no improvement in cancer-free survival.

These studies were done on mostly smokers and former smokers. What about lung cancer? As you can see at 2:46 in my video, population studies suggest tea may be protective, but let’s put it to the test. Seventeen patients with advanced lung cancer were given up to the equivalent of 30 cups of green tea a day, but “[n]o objective responses were seen.” In a study of 49 cancer patients, 21 of whom had lung cancer, the subjects received between 4 and 25 cups worth of green tea compounds a day. Once 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. Indeed, green tea compresses may be able to shorten the duration of the burns, as you can see at 3:21 in my video.

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 10 percent in the untreated control group, which is consistent with the benefits of green tea compounds on cervical cancer cells in a petri dish. When women were given green tea extract pills to take, however, they didn’t seem to help.

I talked about the potential benefit of green tea wraps for skin cancer in Treating Gorlin Syndrome with Green Tea, but is there any other cancer where green tea can come into direct contact? Yes. Colon cancer, which grows from the inner surface of the colon that comes into contact with food and drink. As you can see at 4:13 in my video, 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 one hundred thirty-six patients with a history of polyps were randomized to get green tea extract pills or not. Now, this study was done in Japan, where drinking green tea is commonplace, so, effectively, this was comparing those who drank three cups of green tea a day to subjects who drank four daily cups. A year later on colonoscopy, the added-green tea group had only half the polyp recurrence and the polyps that did grow were 25 percent smaller. With such exciting findings, why hasn’t a larger follow-up study been done? Perhaps due to the difficulty “in raising funds” for the study, “because green tea is a beverage but not a pharmaceutical.”

There is good news. 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. I look forward to presenting the results to you when they come in.

What about prostate cancer? See my videos Preventing Prostate Cancer with Green Tea and Treating Prostate Cancer with Green Tea.

You may also be interested in these somewhat older videos:

How interesting was that about wisdom teeth? Green tea can also be used as an anti-cavity mouth rinse, which I discuss in my video What’s the Best Mouthwash?.

Is Caffeinated Tea Dehydrating? Watch the video to find out.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

Treating Prostate Cancer with Green Tea

Green tea has been called nature’s defense against cancer. Population studies linking green tea consumption with lower cancer risk have led some to advocate for the incorporation of green tea into the diet “so as to fully benefit from its anticarcinogenic properties.” What, after all, is the downside?

But, population studies can’t prove cause and effect. Indeed, “it is not possible to determine from these population-based studies whether green tea actually prevents cancer in people”…until it is put to the test.

Prostate cancer is preceded by a precancerous condition known as intraepithelial neoplasia. You can see a graphic of the progression at 0:41 in my video Treating Prostate Cancer with Green Tea. Within one year, about 30 percent of such lesions turn into cancer. Because no treatment is given to patients until cancer is diagnosed, this presents a perfect opportunity to try green tea. In the study, 60 men with precancerous prostate intraepithelial neoplasia were randomized into either a green tea group or a placebo group. Since it’s hard to make a convincing placebo tea, the researchers used green tea pills that were roughly equivalent to about six cups of green tea a day and compared them to sugar pills. Six months into the study, they took biopsies from everyone. In the placebo group, 6 of the 30 men developed cancer by the halfway point and 3 of the remaining 24 developed it by the end of the year. So, 9 out of 30 in the placebo group, about 30 percent, developed cancer within the first year, which is what normally happens without any treatment. In the green tea group, however, none of the 30 men developed cancer within the first six months and only one developed it by the end of the year. Only 1 out of 30 is nearly ten times less than the placebo group. This marked the first demonstration that green tea compounds could be “very effective for treating premalignant lesions before [prostate cancer] develops.” Even a year later, after the subjects stopped the green tea, nearly 90 percent of the original green tea group remained cancer-free, while more than half of the placebo group developed cancer, as you can see at 2:09 in my video. This suggests that the benefits of the green tea may be “long-lasting,” with an overall nearly 80 percent reduction in prostate cancer.

What if you already have prostate cancer? A proprietary green tea extract supplement was given to 26 men with confirmed prostate cancer for an average of about a month before they had their prostates removed, and there was a significant reduction in a number of cancer biomarkers such as PSA levels, suggesting a shrinkage of the tumor. However, there was no control group, and the study was funded by the supplement company itself. When an independent group of researchers tried to replicate the results in a randomized, double-blind, placebo-controlled trial, they failed to find any statistically significant improvement. Perhaps green tea is only effective in the precancerous state and not powerful enough “to meaningfully impact overt prostate cancer”?

It certainly didn’t seem to help for advanced metastatic cancer in the two studies that tried it. What’s more, doubt has recently been cast on the precancerous results. When researchers tried to replicate it, the green tea extract group only seemed to cut prostate cancer development about in half, which very well may have happened just by chance, given the small number of people in the study. So where does that leave us?

Unfortunately, green tea extract pills are not without risk. There have been about a dozen case reports of liver damage associated with their use. Until there’s more solid evidence of benefit, I’d stick with just drinking the tea. Green or black? A recent study that randomized about a hundred men with prostate cancer to consume six cups a day of green tea or black tea found a significant drop in PSA levels and NF-kB in the green tea group, but not in either the black tea or control groups, as you can see at 4:12 in my video. NF-kB is thought to be a prognostic marker for prostate cancer progression, so the green tea did appear to work better than the black tea.

What happens if we pack our diet with all sorts of plant foods? See my Cancer Reversal Through Diet? video.

Before and after: Learn about Preventing Prostate Cancer with Green Tea and Changing a Man’s Diet After a Prostate Cancer Diagnosis.

Similar studies were done with pomegranates. I discuss the results in Pomegranate vs. Placebo for Prostate Cancer.

Interested in other ways to prevent or treat prostate cancer? See:

What about green tea and other types of cancer? Check out:

For more on some of green tea’s other benefits, see:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations: