Probiotics 'may improve blood pressure'

“Eating probiotics may lower blood pressure,” The Daily Telegraph reports.

Probiotics, so-called “friendly bacteria”, have been found to moderately reduce blood pressure in a new study.

The study is what is known as a systematic review, which is essentially a study of studies. Researchers combined the results of nine randomised controlled trials (regarded as the “gold standard” in evidence-based medicine).

The results suggest that probiotics led to a modest but significant reduction in blood pressure.

The reliability of any systematic review depends on the included studies, and the researchers point out that there were some weaknesses in the studies they included. For example, six of the trials were only conducted on 20 to 40 people. With such a small sample size, any effect on blood pressure could have been the result of chance.

As the lead researcher is quoted as saying in the media, more research is required before doctors can confidently recommend probiotics for high blood pressure control and prevention.

Proven methods to improve blood pressure levels include quitting smoking, sticking to the recommended levels of alcohol consumption, eating a healthy diet (in particular, reducing salt consumption) and taking regular exercise.

Where did the story come from?

The study was carried out by researchers from Griffith University and Gold Coast Health, Australia. No source of funding was reported.

The study was published in the peer-reviewed medical journal Hypertension.

The story was accurately reported in the media, though the Daily Express’s claims that eating “a pot a day [could] … help save your life” is probably overstating the findings of the study.

What kind of research was this?

This was a systematic review and meta-analysis that aimed to determine the effect of probiotic consumption on blood pressure. Systematic reviews aim to identify all the evidence related to a specific research question and synthesise the findings from individual studies or reports in an unbiased way. Meta-analysis is a mathematical technique for combining the results of individual studies to arrive at one overall measure of the effect of a treatment.

The researchers also aimed to use their results to provide information on the most effective probiotic and dose, and how long probiotics need to be taken.

A systematic review, when performed well, should give the best possible estimate of the true effect of probiotics on blood pressure.

What did the research involve?

The researchers searched databases of published literature and trials to identify randomised controlled trials (RCTs) that had given people probiotics and had assessed the effect on blood pressure.

Once they had identified relevant trials, the researchers assessed them to see if they were well-performed and extracted data.

The results of all the trials were then combined to produce a "bottom line" on the effectiveness of probiotics on blood pressure.

What were the basic results?

The researchers included nine RCTs with 543 participants in total. Six of the trials had between 20 and 40 participants.

Some trials involved healthy people, others included patients with hypertension (high blood pressure), hypercholesterolemia (high levels of cholesterol in the blood), metabolic syndrome (a combination of diabetes, high blood pressure and obesity) or who were overweight or obese. The species and dose of probiotics used, and how they were given, also varied across the trials.

Trials used either yoghurt, fermented and sour milk, probiotic cheese, encapsulated supplements or rose-hip drinks.

The trials gave people between a single species and three species of probiotic at the same time, and the daily dose of probiotics varied between 109 colony-forming units and 1012 colony-forming units. A colony-forming unit is an estimate of the amount of micro-organisms, usually bacteria or fungi, in a given sample.

The duration of the trials varied from three weeks to nine weeks.

After combining the results of the trials the researchers found that:

Probiotic consumption significantly reduced systolic blood pressure by 3.56 mm Hg compared to control (systolic blood pressure is the "top" number and is the blood pressure in the arteries when the heart beats).
Probiotic consumption significantly reduced diastolic blood pressure by 2.38 mm Hg compared to control (diastolic blood pressure is the "bottom" number and is the blood pressure in the arteries between heart beats).

By combining the results of different sub-groups of studies they found that:

Using dairy products as the source of probiotics resulted in significant reductions in systolic and diastolic blood pressure, whereas using other sources of probiotics did not.
Using multiple species of probiotics resulted in significant reductions in systolic and diastolic blood pressure, whereas using a single species did not.
Using a dose of at least 1011 colony-forming units per day resulted in significant reductions in systolic and diastolic blood pressure, whereas using lower doses did not.
Taking probiotics for at least eight weeks resulted in significant reductions in systolic and diastolic blood pressure, whereas taking probiotics for shorter periods did not.
People who had blood pressure of 130/85 mm Hg (higher than ideal but still normal) or higher had significant improvements in diastolic blood pressure but people with blood pressure less than 130/85 mm Hg did not.

How did the researchers interpret the results?

The researchers concluded that their results suggest consuming probiotics may improve blood pressure by a modest degree, and that this effect may be greater if blood pressure is high to begin with, multiple species of probiotics are consumed, probiotics are taken for eight weeks or longer, and if each dose contains at least 1011 colony-forming units.

They go on to say that “the reduction [in blood pressure] reported in this meta-analysis is modest; however, even a small reduction of [blood pressure] may have important public health benefits and cardiovascular consequences.”

Conclusion

This systematic review and meta-analysis has found that probiotic consumption results in moderate reductions in blood pressure.

The results of a systematic review depend on the included studies, and the researchers point out that there were some weaknesses in the studies they included. They say that “more randomised, controlled studies with larger sample groups, longer durations and adequate blinding of conditions trials are needed to confirm the effect of different probiotic species and products on BP [blood pressure] and hypertension.”

Analysis of subgroups of studies led the researchers to conclude that blood pressure improvements may be greater among those with elevated blood pressure, when the daily dose of probiotics is at least 1011 colony-forming units, when more than one species of probiotic is taken and when probiotics are taken for at least eight weeks.

However, they also point out that these conclusions are based on the results of only a few studies, and the majority of them were very small – six of the trials were only conducted on between 20 and 40 people.