Flavonoid-rich foods like berries, apples, pears, and wine appear to have a positive effect on blood pressure levels. This association is also partially explained by characteristics of the gut microbiome, according to a recent study published in Hypertension. [1] Past studies have provided strong evidence that the composition of the gut microbiome can partly explain the association between dietary flavonoids and cardiovascular health, but the present study is the first to provide data demonstrating how the gut microbiome may explain the associations between dietary flavonoid intake, flavonoid-rich foods, and blood pressure.

What are flavonoids?

Dietary flavonoids are plant-derived compounds commonly found in fruits, vegetables, tea, chocolate, and red wine. Flavonoids are predominantly broken down by the gut microbiome and have been shown to have a positive effect on cardiovascular health.[2,3] The present study found that consuming even small amounts of flavonoid-rich foods can significantly lower blood pressure.[1] Dietary flavonoids have probiotic-like properties that can stimulate the growth of certain gut bacteria, and this microbiome effect appears to play a role in moderating blood pressure.[4] However, researchers are still exploring the biological mechanisms of flavonoids and how the gut microbiome plays a role in affecting health outcomes. 

What did the study investigate?

Researchers at the Institute for Global Food Security at Queen’s University in Belfast, Northern Ireland recruited 904 adults (57% men, 43% women) ​​from Germany's PopGen biobank. Upon enrollment, participant characteristics like sex, age, smoking status, medication use, and physical activity were collected. Participants' blood pressure, food intake, and gut microbiome composition were evaluated at regular follow-up examinations. Gut microbiome composition was assessed by fecal bacterial DNA extracted from stool samples. Self-reported food frequency questionnaires were completed by participants to determine their flavonoid-rich food intake during the previous year. Here’s what the analysis comparing regular flavonoid intake with gut microbiome and blood pressure levels found:

The gut microbiome plays a key role in metabolizing flavonoids to enhance their cardioprotective effects

Participants in the study who had the highest intake of flavonoid-rich foods—including berries, red wine, apples, and pears—had greater gut microbial diversity and lower systolic blood pressure levels than participants who consumed the lowest levels of flavonoid-rich foods. 

These blood pressure lowering effects were achieved through simple daily dietary changes. Eating ~1.5 servings of berries per day was associated with a 4.1 mmHg reduction in systolic BP, and the researchers found that 12% of this association was explained by gut microbiome factors. Drinking ~3 glasses per week of red wine was also associated with 3.7 mmHg lower systolic BP levels. Researchers suggest that up to 15% of this association could be explained by the gut microbiome. 

What do the findings tell us about flavonoids, gut composition, and heart health?

The gut microbiome plays a key role in metabolizing flavonoids—and enabling the enhanced cardioprotective effects for which they're so well-known. This study provides strong evidence to suggest that the blood-pressure-lowering effects of high flavonoid consumption are: 1) relatively simple to achieve through daily diet changes and 2) modified by the microbiome. Increasing intake of berries, red wine, apples, and pears can lead to increased flavonoid intake, improved microbiome composition, and (in some cases) lower blood pressure. 

What do these findings mean for future research?

According to lead investigator Professor Aedín Cassidy, Chair of Nutrition & Preventive Medicine at the Institute for Global Food Security, “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.” Metabolic profiles can vary substantially between people due to residual or unmeasured confounding factors such as other health conditions or genetics. This variation may lead to bias, and should therefore be accounted for in future studies.

Furthermore, food frequency questionnaires do not always capture the total diet and can be prone to measurement error, which can lead to inaccuracies, particularly in the intake of nutrients like flavonoids. Future studies may want to use professionally-administered diet assessment tools like 24-hour recalls to reduce reporting bias.

Key Takeaways

• The gut microbiome plays a key role in metabolizing flavonoids to enhance their cardio-protective effects.
• The benefits of flavonoids can partly be explained by greater gut microbiome diversity.
• Consuming flavonoid-rich foods may help lower blood pressure levels and reduce cardiovascular disease risk.
• The blood-pressure-lowering effects of high flavonoid consumption can be achieved through changes to your daily diet.

Marianna Moore, MS, CSCS

References

[1]https://pubmed.ncbi.nlm.nih.gov/34420369/

[2]https://pubmed.ncbi.nlm.nih.gov/23576043/

[3]https://www.mdpi.com/1420-3049/23/4/898

[4]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7211351/