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Should you take probiotics to lower high blood pressure?

I’m always a little wary of reporting about the health benefits of consuming beneficial bacteria — known as probiotics — because studies have flip-flopped so much on whether they’re helpful or useless. (For example, this study found that taking probiotic supplements prevents diarrhea caused by antibiotics, while this one found no benefits.)

But a new review of nine clinical trials published Monday in the journal Hypertension that found taking probotics led to moderate reductions in high blood pressure certainly looks promising. The Austrialian researchers analyzed all the research data and found that taking a probiotic supplement reduced systolic blood pressure (the top number) by an average of 3.56 mm Hg and diastolic blood pressure (the bottom number) by an average of 2.38 mm Hg compared to taking a placebo.

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“The small collection of studies we looked at suggest regular consumption of probiotics can be part of a healthy lifestyle to help reduce high blood pressure, as well as maintain healthy blood pressure levels,” study leader Jing Sun, a senior lecturer at the Griffith Health Institute and School of Medicine in Queensland, Australia, said in a statement.

Case closed, right? Well, not exactly.

Some studies led to far more dramatic improvements in blood pressure than others. Supplements needed to be taken for at least 8 weeks and contain a variety of beneficial bacteria to get significant benefits. Beneficial bacteria packaged in capsule form didn’t work nearly as well as those mixed into milk, yogurt, or cheese.

“There are a lot of different types of probiotics, and researchers are still rying to figure out which types are most beneficial for preventing heart disease” as well as other health problems, said Kerry Ivey, a post-doctoral research scientist at the Harvard School of Public Health.

Ivey recently conducted a small clinical trial to see whether probiotics mixed into yogurt worked better than probiotic capsules for lowering high blood pressure, but the findings haven’t yet been published.

Researchers have been eagerly studying the microbiome of 500 trillion organisms that live in our intestinal tract to glean insights into how a healthful balance might protect against a wide range of diseases, but they still have more questions than answers.

“I think the whole idea of gut organisms is a wonderful huge next frontier in terms of health and disease,” said Dr. Thomas Moore, associate provost at Boston University Medical Campus, who helped determine that the Dietary Approach to Stop Hypertension or DASH diet was an effective way to lower blood pressure.

If probiotics are still a frontier, then scientists in this field are pioneers, testing various combinations of beneficial bacteria to see which ones, if any, work and for which condition.

Ivey pointed out that physician groups, for the most part, haven’t included probiotics in their practice guidelines because of the current lack of evidence that they work; probiotics are only recommended by two surgical societies to use after specific gastrointestinal surgeries.

The amount of variety in probiotic formulations could account for the conflicting study findings, but Moore thinks there might be an alternative explanation for the large differences seen among probiotics in the blood pressure lowering study.

When certain beneficial bacteria like lactobacilli are added to milk or other dairy products, the fermentation products they produce have been shown to have similar effects on blood vessels as ACE inhibitors, drugs prescribed by doctors to manage hypertension.

Thus, it could be the compound formed in the dairy product itself — rather than the good bacteria colonizing the intestinal tract — that lowers blood pressure.

In their study, the researchers pointed to this as one explanation but also said probiotics could work within the intestinal tract to improve blood pressure by helping to regulate the hormone system that controls blood pressure and fluid balance.

An exact mechanism for how probiotics work within the body might never be fully understood even if evidence accumulates to the point that doctors start to routinely recommend certain formulations to patients.

But Moore pointed out that he still can’t explain how the DASH diet — based on fruits, vegetables, legumes, and whole-grains with little red meat or sweets — works to lower blood pressure.

“It’s one of the most common questions we get asked, is how does the DASH diet work,” Moore said. “And the short right answer is: we have no clue.”

Deborah Kotz can be reached at dkotz@globe.com. Follow her on Twitter @debkotz2.
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