The Power of Tea

Hello and welcome to the Nutrition Facts podcast. I’m your host, Dr. Michael Greger. 

Now, I know I’m known for explaining how not to do certain things (just look at my books, How Not to Die, the one I’m working on right now–How Not to Diet), but what I actually have to share with you is quite positive and boils down to this: What’s the best way to live a healthy life?  Here, are some answers.

Today, we raise a glass to the power of tea. It is getting to be iced tea weather.  Great way to flood your body with phytonutrients throughout the day! Green tea has been tested to try to stop and reverse the progression of oral cancer, lung cancer, cervical cancer, colon cancer.  What did they find? 

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 finger paint 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—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 3,4-DHPA. 

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. That’s pretty exciting. 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. I look forward to presenting the results when they come in.

How do the blood-pressure lowering effects of hibiscus tea compare to the DASH diet, a plant-based diet, and a long-distance endurance exercise?

The latest research pitted hibiscus against obesity, giving hibiscus to overweight individuals, and showed reduced body weight, but after 12 weeks on hibiscus they only lost like 3 pounds, and really only one and a half pounds over placebo—clearly no magic fix.

The purported cholesterol-lowering property of hibiscus tea had looked a bit more promising. Some older studies suggested as much as an 8% reduction drinking two cups a day for a month, but when all the studies are put together the results were pretty much a wash. This may be because only about 50% of people respond at all to drinking the equivalent of between 2 to 5 cups a day, though those that do respond may get a respectable 12 or so percent drop in cholesterol, but nothing like the 30% drop one can get within weeks of eating a healthy enough plant-based diet.

High blood pressure is where hibiscus may really shine, a disease affecting a billion people, killing millions. Up until 2010, there wasn’t sufficient high quality research out there to support the use of hibiscus tea to treat it, but there are now randomized, double-blind, placebo-controlled studies where hibiscus tea is compared to artificially colored and flavored water that looks and tastes like hibiscus tea, and the tea did significantly better.

We’re still not sure why it works, but hibiscus does appear to boost nitric oxide production, which could help our arteries relax and dilate better. Regardless, an updated review acknowledged that the daily consumption of hibiscus tea may indeed significantly lower blood pressures in people with hypertension, but by how much? How does this drop in blood pressure compare to that of other interventions?

Well, the premier clinical trial when it comes to comprehensive lifestyle modification for blood pressure control is the PREMIER clinical trial. Realizing that 9 out of 10 Americans are going to develop hypertension, they randomized 800 men and women with high blood pressure into one of three groups. One was the control group, the so-called advice only group, where patients were just told to lose weight, cut down on salt, increase exercise and eat healthier, here’s a brochure. In the two behavioral intervention groups they got serious; 18 face-to-face sessions, group meetings, food diaries, monitored physical activity, calorie and sodium intake. Now, one intervention group just concentrated on exercise and the other one included exercise and diet. They pushed the DASH diet, high in fruits and vegetables, and low in full-fat dairy products and meat. And in 6 months achieved a 4.3 point drop in systolic blood pressure, compared to control, slightly better than the lifestyle intervention without the diet. Now a few points might not sound like a lot—that’s like someone going from a blood pressure of 150 over 90 to a blood pressure of 146 over 90—but on a population scale a 5-point drop in the total number could result in 14% fewer stroke deaths, 9% fewer fatal heart attacks, and 7% fewer deaths every year overall.

But, a cup of hibiscus tea with each meal didn’t just lower blood pressure by 3, 4 or 5 points but by 7 points, 129 down to 122. And, in fact, tested head-to-head against a leading blood-pressure drug called captopril, two cups of strong hibiscus tea every morning, using a total of 5 tea bags for those 2 cups, was as effective in lowering blood pressure as a starting dose of 25 mg of captopril taken twice a day.

So, as good as drugs, without the drug side-effects, and better than diet and exercise? Well, the lifestyle interventions were pretty wimpy. As public health experts noted, the PREMIER study was only asking for 30 minutes of exercise a day, whereas the World Health Organization is more like an hour a day minimum.

And diet-wise, the lower the animal fat intake, and the more plant sources of protein the PREMIER participants were eating, the better the diet appeared to work, which may explain why vegetarian diets appear to work even better, and the more plant-based the lower the prevalence of hypertension.

On the DASH diet, they were told to cut down on meat, but were still eating meat every day, so would qualify as nonvegetarians.  Here, in the Adventist 2 study, which looked at 89,000 Californians and found that those who instead only ate meat on more like a weekly basis had 23% lower rates of high blood pressure. Cut out all meat except fish and the rate is 38% lower. Cut out all meat period—the vegetarians have less than half the rate and the vegans—cutting out all animal protein and fat—appeared to have thrown three quarters of their risk of this major killer out the window.

One sees the same kind of step-wise drop in diabetes rates as one’s diet gets more and more plant-based and a drop in excess body weight such that only those eating completely plant-based diets fell into the ideal weight category. But could that be why those eating plant-based diets have such great blood pressure? Maybe it’s just because they’re so skinny on average. I’ve shown previously how those eating plant-based diets have just a fraction of the diabetes risk even at the same weight, even after controlling for BMI, but what about hypertension?

The average American has what’s called prehypertension, which means the top number of your blood pressure is between 120 and 139. Not yet hypertension, which starts at 140, but it means we may be well on our way.

Compare that to the blood pressure of those eating whole food plant-based diets. Not 3 points lower, 4 points lower, or even 7 points lower, but 28 points lower. Now, but the group here eating the standard American diet was, on average, overweight with a BMI over 26, still better than most Americans, while the vegans were a trim 21—that’s 36 pounds lighter.

So maybe the only reason those eating meat, eggs, dairy, and processed junk had such higher blood pressure was because they were overweight, maybe the diet per se had nothing to do with it.

To solve that riddle we would have to find a group still eating the standard American diet but as slim as a vegan. To find a group that fit and trim, they had to use long-distance endurance athletes, who ate the same crappy American diet — but ran an average of 48 miles per week for 21 years. They ran almost 2 marathons a week for 20 years; so, if you do that, anyone can be as slim as a vegan—no matter what they eat. Both the vegans and the conventional diet group were sedentary—less than an hour of exercise a week.

So, it appears if you run an about a thousand miles every year you can start to rival some couch potato vegans. Doesn’t mean you can’t do both, but it may be easier to just eat plants.

Adding milk to tea can block its beneficial effects, potentially explaining why green tea drinkers appear to be better protected than consumers of black tea.

Our endothelium, the inner lining of our blood vessels that controls the function of every artery in our body, appears to play a critical role in a variety of human disorders, including peripheral vascular disease, stroke, heart disease, diabetes, kidney failure, cancer, and blood clots.

Unfortunately, endothelial cells only live about 30 years, and their replacements don’t seem to function as well. So, as men and women approach the ages of 40 and 50, there is a progressive decline in endothelial function. At age 50 or 60, we can no longer tolerate the risk-factor burden that we were once able to tolerate as teenagers, thanks to this progressive decline in endothelial function. But that’s what we used to think.

There are increasing data to suggest that age is not an immutable risk factor. In a Chinese population study, for example, they did not see the progressive decline.  The older Chinese in their 60’s had the arterial function of young folks in their 20’s. These data suggest that progressive endothelial dysfunction is not an inevitable consequence of aging but might be related to prolonged exposure to environmental factors more prevalent in Westernized countries than in China. What could it be? Well, traditional Chinese diets include green tea, which has been shown to have a beneficial effect on endothelial function within 30 minutes of consumption, and lasting about two hours. It wasn’t the caffeine, which alone had no effect. They suspect it is the flavonoid phytonutrients in the tea leaves.

Black tea appears to work about just as well as green tea, but then, why is green tea associated with lower heart disease risk, but black tea not? In fact, in two British studies, tea consumption was associated with increased risk of coronary artery disease. Maybe it’s because the Brits drink their tea with milk, whereas green tea is typically drunk straight. If only there was a country that drank black tea, but without milk. There is, the Netherlands, and in those studies, black tea was associated with the same drop in risk as the green tea studies; so, maybe it is the milk. But you really can’t know until you put it to the test.

They found the addition of milk to black tea completely prevents the biological activity of tea in terms of improvement of endothelial function. And so, that could explain it. It appears casein is the culprit (the milk protein—casein), though soy protein was recently found to have the same nutrient binding effect.

The European Society of Cardiology issued a press release about the study showing the protective effect of tea was totally wiped out by adding milk, and suggested consumers should consider cutting down. Milk-drinkers were not amused, “as long as the reported results are not confirmed in a fair number of humans who drink their tea outside the lab setting, we will continue to add milk to ours.”

The researchers responded, challenging the notion that their study wasn’t big enough. They had 16 people, and the results were highly significant. Across those 16 people, the addition of milk to tea not only reduced, but completely blunted the effects of the tea. And, uh, the rationale for drinking tea in a lab setting was because they were doing an experiment. Were they supposed to drag the equipment to a Starbucks or something?

As doctors, the milky tea drinkers asserted, just as we would not prescribe a new drug to patients if it was studied only in one small study, milk abstinence should not be recommended to tea drinkers, apparently forgetting that the reason we don’t prescribe drugs without overwhelming evidence is because drugs can kill.  So, the benefits better outweigh the risks, but what’s the downside of a little milk abstinence?

To see any graphs, charts, graphics, images or studies mentioned here, please go to the Nutrition Facts podcast landing page.  There, you’ll find all the detailed information you need – plus links to all the sources we cite for each of these topics.

Be sure to check out my new How Not to Die Cookbook.It’s beautifully designed, with more than 120 recipes for delicious, plant-based meals, snacks and beverages.  All the proceeds from the sales of all my books all go to charity.  I just want you to be healthier.  

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Thanks for listening to Nutrition Facts.  I’m Dr. Michael Greger.

This is just an approximation of the audio content, contributed by Allyson Burnett.