What does your gut say about your heart? According to new research, nutritional scientists found that the trillions of microbes that live in our digestive tract, collectively known as the gut microbiome, are partly responsible for the association between moderate wine consumption and lower blood pressure.
Although previous studies have shown the benefits of a more diverse gut microbiome, this is the first study that examines how gut microbiota may provide a link between lower blood pressure and eating and drinking flavonoid-rich foods such as berries and red wine.
The study, published last week in Hypertension, an American Heart Association journal, collected data from the PopGen cohort of Northern Germany, which included more than 1,000 participants aged 25 to 82. Research teams from Queen's University Belfast (QUB) and Kiel University in Germany conducted follow-up examinations, completing detailed questionnaires on participants' diets, collecting fecal bacterial DNA through stool samples and measuring systolic and diastolic blood pressure three times per session with digital monitors.
Scientists have repeatedly found links between the polyphenols in plant foods and wines and better cardiovascular health. But a key question is how the body metabolizes these substances. Recent studies have found a link between gut microbiota, the microorganisms in the human digestive tract and cardiovascular disease. And a prior analysis of data from the same PopGen cohort found that up to 18.5 percent of the association between habitual consumption of flavonoid-rich foods and abdominal fat could be explained by microbial diversity and abundance of beneficial stomach bacteria such as lactobacillus, ruminococcaceae and oscillibacter.
For this study, the researchers focused on six different flavonoid subclasses: flavanones, anthocyanins, flavan-3-ols (flavanols), flavonols, flavones and polymeric flavonoids. All of these are organic compounds found in plants. According to Dr. Aedín Cassidy, lead author and professor at QUB School of Biological Sciences, studies suggest the main subclasses associated with cardiovascular benefits are the anthocyanins (berries and black currants), flavanols (dark chocolate, tea, apples and red wine) and flavonols (onions, tea, grapes and red wine).
The researchers found that greater consumption of flavanols was associated with lower systolic blood pressure while greater consumption of flavonols and flavones was associated with lower pulse pressure. Greater consumption of berries and red wine was also linked to a more diverse gut microbiome.
"We were surprised at how important the microbiome was," Dr. Cassidy told Wine Spectator via email. "Unlike many other food constituents, the 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. Up to 15.2 percent of the association between flavonoid-rich foods and systolic blood pressure could be explained by the diversity found in participants' gut microbiome." She adds that drinking 250ml of red wine a week, about two glasses, was associated with an average of 3.7mm Hg lower systolic blood pressure level, of which 15 percent could be explained by the gut microbiome.
How does the gut explain heart benefits? The researchers looked at flavonoid consumption and gut bacteria diversity and abundance, which are directly associated, then assessed the relationship between these microbial factors and blood pressure. They presented results as a percentage: the association between flavonoid intake and blood pressure mediated by the microbiome, to the total association between flavonoid intake and the microbiome on blood pressure. Dr. Cassidy's 15.2 percent figure could be explained by a combination of microbiome diversity and higher relative abundance of ruminococcaceae.
"Gut microbiota is highly variable between individuals, and there are reported differences in gut microbial compositions among people with and without cardiovascular disease," Cassidy said. "Higher microbiome diversity was associated with lower systolic blood pressure."
The authors add that a better understanding of the mechanisms underlying associations between diet and blood pressure will allow more effective and precise dietary approaches for the prevention of hypertension.
Although the findings are promising for wine lovers, Dr. Cassidy suggests the scientific community needs clinical trials to confirm the link between diverse gut microbiota, polyphenol-rich diets and lower risk of cardiovascular disease. Trials could reveal a cause-and-effect explanation rather than an association.
"Our gut microbiome plays a key role in metabolizing flavonoids to enhance their cardioprotective effects," Dr. Cassidy says. "This study provides evidence to suggest these blood pressure–lowering effects are achievable with simple changes to the daily diet."