Data published in Nutrients indicated 73% of participants in the blueberry powder group experienced improvements in endothelial function, while 61% of the placebo displayed a decrease in endothelial function.
However, no benefits were observed for blood pressure, report scientists from Louisiana State University System, Southeast Louisiana Veterans Health Care System, and the University of Pennsylvania.
“[T]here was evidence of improved vascular health with the demonstration that endothelial function was improved (i.e., increased),” wrote the authors, led by April Stull. “This indicates that consumption of blueberries may increase endothelial function, even though blood pressure and other variables studied were not significantly affected.
“Although more validation trials are needed to fully evaluate this observation, our study does suggest a favorable benefit of blueberries on vascular health over a six-week period in adults with metabolic syndrome.”
Endothelial dysfunction may play an important role in the increases in blood pressure that occur after menopause. Further, endothelial dysfunction is known to increase arterial stiffness, which is involved in the development and progression of both hypertension and cardiovascular disease.
The beneficial effects of the blueberries are thought to be linked to their flavonoid content - in particular anthocyanins and flavanols.
Consumer interest in blueberries and the compounds they contain has increased in recent years, following results from studies reporting a wide range of health benefits, most notably for brain health and reducing the risk of cognitive decline.
This is not the first report of potential endothelial benefits, with “compelling” data published in the American Journal of Clinical Nutrition (2013, Vol. 98, pp. 1179-1191) indicating that blueberry flavonoids could boost endothelial function and enhance heart health.
For the new study, the researchers provided daily doses of 45 grams of freeze-dried blueberry powder made from an equal mixture of the highbush blueberries Tifblue (Vaccinium ashei) and Rubel (Vaccinium corymbosum). This dose provided 581 mg of anthocyanins and 1,547 mg of total polyphenol bioactives, said the researchers.
Stull and her co-workers recruited 44 adults to participate in their study. The volunteers were randomly assigned to receive two smoothies per day with or without blueberry powder for six weeks.
Results showed that while neither blood pressure nor insulin sensitivity were affected by the intervention, a significant improvement in endothelial function was observed for participants in the blueberry group.
While this study did not find evidence of blood pressure benefits, data from an eight week study indicated that freeze-dried blueberry powder (22 grams per day) resulted in 5.1% and 6.3% reductions in systolic and diastolic blood pressure (Journal of the Academy of Nutrition and Dietetics, doi: 10.1016/j.jand.2014.11.001).
“It is possible that a longer study duration would have led to improvements in both endothelial function and blood pressure,” wrote Stull and her co-authors. “Researchers have found that blueberries improved both blood pressure and endothelial function or a biomarker of endothelial function (i.e., nitric oxide) over a study duration of 8–12 weeks.
“It is important to note that even though previous studies observed positive changes in both endothelial function and blood pressure with a longer duration than the current study, one consideration to explain our findings is that the majority of the participants in our trial were on antihypertensive medication, which was part of our inclusion criteria for metabolic syndrome.
“[C]linical trials with a longer duration (greater than 8–12 weeks) evaluating the effects of blueberries or anthocyanin-rich foods on endothelial function and blood pressure prior to the study, mid-study and end of the study are warranted to explain the potential role in improving endothelial function and blood pressure in a population at high risk for developing CVD.”
2015, Volume 7, Number 6, Pages 4107-4123; doi:10.3390/nu7064107
“Blueberries Improve Endothelial Function, but Not Blood Pressure, in Adults with Metabolic Syndrome: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial”
Authors: A.J. Stull, K.C. Cash, C.M. Champagne, et al.