Have you ever wondered if there’s a natural way to lower your high blood pressure, guard against Alzheimer's, lose weight, and feel better? Well as it turns out there is. Michael Greger, M.D. FACLM, founder of NutritionFacts.org, and author of the instant New York Times bestseller “How Not to Die” celebrates evidence-based nutrition to add years to our life and life to our years.

The Flower Power of Hibiscus Tea

The hibiscus plant has flamboyant, beautiful flowers and real health benefits. This episode features audio from:

  • https://nutritionfacts.org/video/fat-blocking-benefits-of-hibiscus-tea/
  • https://nutritionfacts.org/video/hibiscus-tea-vs-plant-based-diets-for-hypertension/
  • https://nutritionfacts.org/video/how-much-hibiscus-tea-is-too-much/

Visit the video pages for all sources and doctor’s notes related to this podcast.


Today, we revel in the antioxidant properties of hibiscus tea, which, compared to 280 common beverages, ranks number one for its antioxidant content, even beating out the oft-lauded green tea. In our first story, we look at the results of a randomized, double-blind, placebo-controlled trial of hibiscus tea for weight loss.

Hibiscus tea, also known as roselle or Jamaica, is enjoyed around the world hot or cold for its bright red color and tart cranberry-like flavor. It’s the “zing” in Red Zinger tea. I talk about its benefits in the chapter on high blood pressure in How Not to Die––working as well as some leading antihypertensive medications in head-to-head tests, or even beating the drugs out.

Within three hours of drinking hibiscus tea, changes in hundreds of metabolites can be detected in the human bloodstream with “creative” names like hibiscic acid, or hibiscin, or hibiscitrin. Alterations in human gene expression at the three-hour mark after drinking it suggest a downregulation of cholesterol synthesis and an improvement in metabolism. But randomized controlled trials failed to consistently find cholesterol-lowering benefits. An interesting side-effect popped up, though: weight loss.

In Mexico, hibiscus tea has been traditionally used for the treatment of obesity, sparking lots of research interest. Computer modeling studies have suggested that certain hibiscus compounds might bind to the fat-digesting enzyme lipase like a lock-and-key. Test tube studies screening a variety of medicinal plants did indeed find hibiscus inhibited lipase more than most of the others, and hibiscus has been found to reduce body fat in hamsters, mice, and rats, increasing fecal fat excretion. But it wasn’t tested in people, until this study published in 2014.

Spoiler alert: Hibiscus can inhibit obesity and fat accumulation—in humans—and improve fatty liver. To create a randomized double-blind trial, instead of trying to create some artificially colored and flavored placebo tea, they dried the hibiscus tea into a powder and put it into capsules. After 12 weeks, there was a greater reduction in waistlines and percent body fat in the hibiscus group, compared to those who got placebo capsules. But the dose they ended up using was the equivalent of about nine cups of hibiscus tea a day. I recommend people stick to no more than a quart a day on a regular basis, due to the high manganese content. Manganese is an essential trace mineral, but nine cups a day might result in be too much of a good thing.

Finally, in 2018, this study was published using a reasonable dose—the equivalent of about a single 12-ounce glass of hibiscus tea a day. The complicating factor is that they also added lemon verbena to the mix. That’s another herbal tea, better known for improving recovery after intense bouts of strength training, but there were some promising in vitro data on effects of lemon verbena on fat cells in a petri dish. So, they tried a combination. It comes out to be about a cup and a half of hibiscus tea and a quarter cup of lemon verbena tea, once a day, for two months.

Both the tea and placebo groups were fed diets containing the same amount of calories, yet those randomized to the tea group lost significantly more weight—five pounds compared to three pounds. That’s only an extra pound or two a month, but an extra pound a month eating the same number of calories. That’s the advantage of fat-blocking interventions that actually cause you to lose more calories, beyond just reducing hunger and making you feel fuller longer in hopes that you’ll eat fewer calories in the first place.

Why not just pop pills instead of brewing tea? There are all sorts of herbal extract supplements on the market, but that presumes we know enough to extract out the right active ingredients. For example, it does not appear to be the red anthocyanin pigments in hibiscus, since white varieties seem to have similar effects. When the various compounds in hibiscus tea are isolated out and tested in various combinations, synergistic effects are found, meaning the whole may be greater than the sum of its parts. As with any sour food or beverage, though (like after eating citrus) it’s important to wash the natural acids off your teeth by rinsing your mouth out with water to protect your tooth enamel. You also want to wait at least an hour before brushing, so as not to erode your enamel when it’s in a softened state.

In our next story, we look at how the blood-pressure lowering effects of hibiscus tea compared to the DASH diet, a plant-based diet, and 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 may get a respectable 12 or so percent drop, but nothing like the 30% 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 and 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?

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. But in the two behavioral intervention groups they got serious. 18 face-to-face sessions, groups meetings, food diaries, monitored physical activity, calorie and sodium intake. One intervention group just concentrated on exercise and the other 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 six months they achieved a 4.3 point drop in systolic blood pressure, compared to the 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 would result in a 14 percent fewer stroke deaths, 9 percent fewer fatal heart attacks, and 7 percent 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, captopril, two cups of strong hibiscus tea every morning, using a total of five tea bags for those two cups, was as effective in lowering blood pressure as a starting dose of 25mg 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 cut down on meat, but are still eating it 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 for 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 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 just have 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 a week for 21 years. You run almost two marathons a week for 20 years anyone can be as slim as a vegan—no matter what you eat.

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

Finally today, the impressive manganese content of hibiscus tea may be the limiting factor for safe daily levels of consumption.

Over-the-counter antacids are probably the most important source for human aluminum exposure in terms of dose. Maalox, for example, taken as directed, can exceed the daily safety limit more than 100-fold, and nowhere on the label does it say to not take it with acidic beverages such as fruit juice. Washing an antacid down with orange juice can increase aluminum absorption 8-fold, and citric acid was worse—the acid found naturally concentrated in lemon and limes.

Just as sour fruits can enhance the absorption of iron, which is a good thing, through the same mechanism they may enhance the absorption of aluminum, raising the question what happens when one adds lemon juice to tea? Previously, I concluded that the amount of aluminum in tea is not a problem for most people because it’s not very absorbable, but what if you add lemon? No difference between tea with lemon, tea without lemon, or no tea at all in terms of the amount of aluminum in the bloodstream, suggesting that tea drinking does not significantly contribute to aluminum actually getting inside the body. They’re talking about black tea, green tea, white tea, oolong tea, what about the red zinger herbal tea, hibiscus? The reason it’s called sour tea is because it has natural acids in it like citric acid—might that boost the absorption of any of its aluminum? Well, a greater percentage of aluminum gets from the hibiscus into the tea water, but there’s less aluminum overall. The question is, does the aluminum then get from the tea water into our body? We don’t have that data; so, to be on the safe side we should assume the worst—that is hibiscus tea aluminum, unlike green and black tea aluminum, is completely absorbable. In that case, based on this data and the World Health Organization weekly safety limit we may not want to drink more than 15 cups of hibiscus tea a day, but that’s based on someone who’s about 150 pounds. If you have a 75-pound 10-year-old, a half gallon a day may theoretically be too much. And more extensive testing more recently suggests levels may reach as high as twice as much, so no more than about two quarts a day for adults, or a quart a day for kids every day or for pregnant women. And hibiscus tea should be completely avoided by infants under 6 months—who should only be getting breast milk anyway—as well as kids with kidney failure, who can’t efficiently excrete it.

The study also raised concern about the impressive manganese level in hibiscus tea. Manganese is an essential trace mineral, a vital component of some of our most important antioxidant enzymes, but we probably only need about 2 to 5 milligrams a day, and 4 cups of hibiscus tea can have as much as 17, averaging about 10. Is that a problem?

Women given 15 cups a day for 4 months, if anything, only saw an improvement in their anti-inflammatory, anti-oxidant enzyme activity. This study using 20 a day similarly showed no adverse short-term effects, and importantly showed that retention of dietary manganese is regulated. Our body’s not stupid; if we take too much in, our body decreases the absorption, and increases the excretion. So, even though tea drinkers may get 10 times more manganese, 10 or 20 milligrams a day, the levels in their blood is essentially identical. So, there is little evidence that dietary manganese poses a risk. That was regular tea, though, we don’t know about the absorption from hibiscus, so to err on the side of caution we should probably not routinely exceed the reference dose of 10 mg per day, so that’s only about a quart a day for adults, a half quart for a 75-pound child. So, that’s actually changed my family’s consumption. Given the benefits of the stuff, I was using it as a substitute for drinking water, so like 2 liters a day, and I was blending the hibiscus petals in, not throwing them away, effectively doubling aluminum content and increasing manganese concentrations by about 30%. So, given this data I’m cutting back to no more than about a quart of filtered hibiscus tea a day.


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