Flavonoid-Rich Foods, Aided by Gut Bacteria, Tied to Lower BP

Fran Lowry

August 23, 2021

A higher intake of flavonoid-rich foods such as berries, apples, tea, and red wine is associated with a clinically relevant reduction in blood pressure levels, an association that is partially explained by bacteria in an individual's gut microbiome, new research suggests.

In a population-based study of more than 900 individuals, those with the highest intake of flavonoid-containing foods had significantly lower systolic blood pressure and pulse pressure, as well as greater gut microbial diversity, compared with those with the lowest intakes.

Up to 15% of this observed association was explained by the gut microbiome, suggesting that these microbes play a key role in metabolizing flavonoids to enhance their cardioprotective effects, according to the researchers.

The study was published online today in the journal Hypertension.

Dr Aedin Cassidy

"We know what we eat plays a critical role in shaping our gut microbiome, but little is known about the relative importance of plant foods and specific constituents called flavonoids," lead researcher Aedin Cassidy, PhD, chair and professor in nutrition and medicine at the Institute for Global Food Security, Queen’s University, Belfast, Northern Ireland, told theheart.org | Medscape Cardiology.

"Unlike many other food constituents, flavonoids are predominantly metabolized in the gut, suggesting that the gut microbiome may be more important in enhancing their biological activity than for other things we eat," Cassidy said.

"There is mounting evidence from population-based studies and clinical trials that a higher intake of flavonoids and flavonoid-rich foods can improve heart health, but for the first time, we provide data highlighting the key role of the gut microbiome in explaining the association between such foods and blood pressure," she noted. "This is one of the first studies to address this."

For this analysis, Cassidy and her group sought to assess to what extent the composition of the gut microbiome might explain the association of habitual flavonoid and flavonoid-rich food intake with systolic and diastolic blood pressure in a community-based sample of 904 individuals aged 25-82 years from Germany's PopGen biobank.

The researchers evaluated participants' food intake, gut microbiome, and blood pressure levels together with other clinical and molecular phenotyping at regular follow-up examinations.

Participants' intake of flavonoid-rich foods during the previous year was calculated from a self-reported food questionnaire detailing the frequency and quantity eaten of 112 foods, and flavonoid values were assigned to foods according to United States Department of Agriculture data on flavonoid content in food.

Participants' gut microbiome was assessed by fecal bacterial DNA extracted from stool samples.

After an overnight fast, participants' blood pressure levels were measured 3 times in 3-minute intervals after an initial 5-minute rest period. Researchers also collected participants diet and lifestyle information.

Analysis of the data showed the following:

  • Eating 1.5 servings of berries per day (about 1 cup) was associated with a 4.1 mm Hg reduction in systolic BP; 12% of this association was explained by gut microbiome factors

  • Drinking 3 glasses of red wine per week was associated with a 3.7 mm Hg reduction in systolic BP; 15% of this association was explained by the gut microbiome.

"These blood pressure-lowering effects are achievable with simple changes to the daily diet," Cassidy said.

"Incorporating flavonoid rich foods into the diet can have clinically relevant reductions in systolic blood pressure and pulse pressure, and a healthy gut microbiome is important to break down flavonoids to a more cardioprotective form," she said.

"Our findings indicate future trials should look at participants according to metabolic profile in order to more accurately study the roles of metabolism and the gut microbiome in regulating the effects of flavonoids on blood pressure," said Cassidy.

"A better understanding of the highly individual variability of flavonoid metabolism could very well explain why some people have greater cardiovascular protection benefits from flavonoid-rich foods than others."

Interesting Data

"The data are interesting," David Jenkins, MD, PhD, DSc, professor of medicine and nutrition at the University of Toronto, Canada, told theheart.org | Medscape Cardiology.

Dr David Jenkins

"Berries and red wine appear to be associated with lower systolic blood pressures. Lower blood pressures have been found in general in people who consume more plant-based diets, especially those high in fruits and vegetables," noted Jenkins, who was not involved with this study.

"Berries and grapes high in polyphenols may have many health benefits as antioxidants and in a recent study have been shown to reduce cardiovascular mortality. The change in chronic microflora is also of interest as this will change with increased fruit and vegetable consumption," he said.

Perhaps one word of caveat, Jenkins added: "Alcohol has been found to increase blood pressure and the risk of stroke. Presumably the beneficial effects as seen here were when wine is consumed in moderation."

Supports Recommendations

The study by Cassidy and colleagues supports the dietary recommendations from the American Heart Association (AHA) for heart health, Penny M. Kris-Etherton, PhD, RDN, professor of nutritional sciences, Penn State University, University Park, Pennsylvania, and chair, AHA Council on Lifestyle and Cardiometabolic Health, told theheart.org | Medscape Cardiology.

"The AHA recommends a healthy dietary pattern that emphasizes a variety of plant foods including fruits, vegetables, whole grains, legumes, nuts, and seeds and is low in sodium, saturated fat, and added sugars. Lean protein foods, including plant protein foods, are recommended, and red meat should be limited. If alcohol is consumed it should be done in moderation," Kris-Etherton said.

"Based on these AHA dietary recommendations, a wide variety of plant foods will promote consumption of many flavonoids that have demonstrated CVD benefits, such as lowering systolic blood pressure as reported by the authors, as well as promoting healthy endothelial function and having anti-thrombotic, anti-inflammatory and antioxidant effects," she said in email.

"This recommended dietary pattern will have other cardiovascular health benefits, such as decreasing LDL cholesterol, due to its very healthy nutrient profile. The exciting new finding reported by Cassidy et al is that the effects of dietary flavonoids on lowering systolic blood pressure are modulated by the gut microbiome," Kris-Etherton said.

"Further research needs to be done to confirm these findings and to identify how different foods affect specific gut bacteria that benefit cardiovascular health."

The research was funded by grants from the German Research Foundation and the German Federal Ministry of Education and Research. Cassidy and Jenkins have disclosed no relevant financial relationships. Kris-Etherton is a spokesperson for the AHA.

Hypertension. Published online August 23, 2021. Full text

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