“Our gut microbiome plays a key role in metabolizing flavonoids to enhance their cardioprotective effects, and this study provides evidence to suggest these blood pressure-lowering effects are achievable with simple changes to the daily diet,” says senior study author Aedín Cassidu, PhD, a professor of nutrition and preventive medicine at the Institute for Global Food Security at Queen’s University in Belfast, Northern Ireland. For the study, researchers examined data on 904 adult participants from the German PopGen biobank network, including information on food intake, gut microbiome, and blood pressure. Participants reported how often they ate 112 different foods, and researchers then used data from the U.S. Department of Agriculture (USDA) to identify flavonoid-rich foods and calculate total daily flavonoid intake. People who had the highest total flavonoid intake had significantly lower average systolic blood pressure — 2.9 millimeters of mercury (mmHg) lower — than people with the smallest amount of flavonoids in their diets, the study found. Participants also provided stool samples, allowing researchers to examine each person’s gut microbiome — the bacteria, microorganisms, fungi, and viruses that are present in the gastrointestinal tract. Up to about 15 percent of the association between certain flavonoid-rich foods, including berries, red wine, apples, and pears, could be explained by greater diversity in the gut microbiome, the study found. In particular, eating 1.6 servings of berries each day (service size 1 cup) was associated with an average reduction in systolic blood pressure of 4.1 mmHg. About 12 percent of this association could be explained by the gut microbiome. And drinking 2.8 glasses of wine (about 4 ounces per glass) each week was associated with an average reduction in systolic blood pressure of 3.7 mmHg. Roughly 15 percent of this connection could be explained by the gut microbiome. “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,” says Dr. Cassidy. The study wasn’t a controlled experiment designed to prove that flavonoids directly cause lower blood pressure. Researchers also limited their analysis to specific flavonoid-rich foods and beverages, and it’s possible that the results might have been influenced by other foods that weren’t examined in the study.
Flavonoids Promote Gut Health
Flavonoids are found naturally in a variety of fruits and vegetables as well as in dark chocolate, tea, and wine. Earlier research has linked flavonoids to lower blood pressure and other markers of cardiovascular health. One study published in the American Journal of Clinical Nutrition examined data on eating habits and blood pressure followed 87,242 women and 23,018 men for more than a decade. None of them had hypertension at the start of the study. By the end, people who had the most flavonoids in their diets — mostly from blueberries and strawberries — were 8 percent less likely to develop high blood pressure. Another study published in the American Journal of Clinical Nutrition examined eating habits, blood pressure, and arterial stiffness for 1,898 women. This study found that women whose diets had the least flavonoids — primarily from berries and tea — had much more arterial stiffness, a risk factor for events like heart attacks and strokes. Higher intake of flavonoids found in berries was also associated with 3.0 mmHg lower average systolic blood pressure. “We are in the early stages of learning about how different foods affect specific gut bacteria and how changes in the gut microbiota affect cardiovascular risk factors and other health measures,” says Penny Kris-Ethertom PHD, RDN, a former chairperson of the American Heart Association’s Lifestyle and Cardiometabolic Health Council Leadership Committee and a nutrition professor at The Pennsylvania State University in University Park, Pennsylvania. “It could be the specific flavonoids present in berries and red wine affected specific gut bacteria, which in turn, affected systolic blood pressure, but more research is needed to understand how certain foods and their flavonoids affect the gut microbiome and how this, in turn, affects blood pressure and other cardiovascular disease risk factors,” says Dr. Kris-Etherton, who wasn’t involved in the new study. Adding more plants to your diet is a good way to consume more flavonoid-rich foods and also promote a healthy, more diverse gut microbiome, says Samantha Heller, RDN, a nutritionist at New York University Langone Medical Center in New York City. “While this study highlights certain foods such as pears, apples, and tea, there is no one magical food that will work miracles,” says Heller, who wasn’t involved in the new study. “All edible plant foods are good and each provides a variety of health benefits.”
