June 5

Flashback Friday: Hibiscus Tea vs. Plant-Based Diets for Hypertension & How Much Is Too Much?


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 we have since seen 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% fewer stroke deaths, 9% fewer fatal heart attacks, and 7% fewer deaths every year overall.

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And 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 5 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. 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.

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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. You run almost two marathons a week for 20 years anyone can be as slim as a vegan—no matter what you eat. So where do they fall on the graph? Both the vegans and the conventional diet group were sedentary—less than an hour of exercise a week.

The endurance runners were here. 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.

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 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—as well as kids with kidney failure, who can’t efficiently excrete it.

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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 the manganese load, 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 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’ve cut back to no more than a quart of filtered a day.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.

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