Montmorency tart cherries reduced systolic blood pressure, insulin levels and insulin concentrations in adults with metabolic syndrome participating in a small pilot study published in the Journal of Functional Foods.
While previous studies on Montmorency tart cherries have explored individual aspects of metabolic syndrome - such as blood pressure and triglycerides - this is the first study to examine the full cluster of conditions that comprise metabolic syndrome, including insulin resistance, hypertension and central obesity, or belly fat. Nearly 35% of U.S. adults are estimated to have metabolic syndrome, which significantly increases the risk of cardiovascular disease and type 2 diabetes.
"Our most noteworthy cardiovascular response observed in the study was the significant reduction in systolic blood pressure for the first two hours after consumption," said lead author Terun Desai, from the School of Life and Medical Sciences at the University of Hertfordshire in Hatfield, UK. "The unique composition of tart cherries, including the synergistic influence of anthocyanins, other polyphenols, and fiber may be a factor."
A group of 11 men and women, ages 37-61, participated in this randomized, placebo-controlled crossover trial. All participants met at least three of the five criteria for metabolic syndrome (waist circumference > 35 inches for women or 40 inches for men, high or borderline high triglyceride levels, low levels of HDL, high blood pressure, and high fasting blood sugar).
During the 6-week study, on three different occasions, each separated by a 14-day washout period, participants consumed either Montmorency tart cherry juice (30 ml of juice concentrate mixed with 100 ml of water), Montmorency tart cherry capsules (10 capsules to match the anthocyanin content of the juice with 130 ml water) or a placebo drink (30 ml of a fruit-flavored syrup mixed with 100 ml of water). The juice contained the equivalent of about 90-110 whole tart cherries and the capsules were made from about 100 whole tart cherries. The placebo drink was matched to the tart cherry juice for calories, taste and visual appearance using maltodextrin (a flavorless carbohydrate), citric acid and red and black food coloring.
Each testing day began between 7:00-10:00 a.m., with participants instructed to fast overnight for at least 10 hours. Height, weight, waist circumference and markers of heart and metabolic health (including arterial stiffness, blood pressure, heart rate, cardiac output, stroke volume, mean arterial pressure, total peripheral resistance, resting metabolic rate, glucose and insulin levels, insulin resistance/sensitivity and blood lipids) were measured at baseline. With the exception of height, weight and waist circumference, these tests were repeated at regular intervals over 5 hours after the drink or capsules were consumed.
The U.K. researchers found Montmorency tart cherry juice led to a significant, clinically-relevant reduction in systolic blood pressure when compared to the placebo 2 hours after consumption, and Montmorency tart cherry juice and Montmorency tart cherry capsules both lowered insulin levels significantly more than the placebo at 1 hour and 3 hours, respectively. Arterial stiffness was also improved 2 hours after consumption of Montmorency tart cherry juice compared to the placebo, however the significance of this finding is unclear as other indicators of vascular stiffness were not improved. No significant differences were found for the other outcomes examined. The results are preliminary and more research is needed with a larger sample size.
"Global rates of metabolic syndrome are on the rise and the results of the present study suggest Montmorency tart cherries, in juice or capsule form, could exert beneficial effects for adults with this condition when incorporated into an overall healthy diet," said Desai.
The researchers also demonstrated that, while certain effects differed at certain points in time, overall responses between Montmorency tart cherry capsules and Montmorency tart cherry juice were not statistically different. This refutes their original hypothesis that capsules may be superior to juice due to an increased bioavailability of anthocyanins. Given this study's acute nature, longer-term research to enhance clinical relevance is warranted.
The study was funded by Heart UK (charity registration No: 1003904).
Montmorency tart cherries are the most common variety of tart cherries grown in the U.S., and are available year-round in dried, frozen, canned, juice and juice concentrate forms. Polyphenols, specifically anthocyanins, give them their ruby-red color and distinctive sour-sweet taste. Other varieties of tart cherries may be imported and not grown locally.