Cocoa flavanols and grape seed extract have earned the attention of leading cardiovascular researchers, whose findings show real promise while pointing back to the kitchen.
The Kuna, who live on islands off the Caribbean coast of Panama, drink cocoa as their main beverage, and many of them have more than five cups a day. Norman Hollenberg, a professor of radiology at Harvard Medical School, found that the island Kuna did not experience the age-related rise in blood pressure common among Americans and Europeans. When several hundred of them moved to Panama City and its suburbs, their blood pressure went up, which pointed to diet and environment as the source of that protection that had prevented the health issues for centuries.
Cocoa flavanols now come in capsule form, sold alongside green tea catechins and french grape seed extract to people hoping to look after their blood vessels, and researchers have since tested their promise well beyond the islands. COSMOS, a trial led by JoAnn Manson and Howard Sesso of the Division of Preventive Medicine at Brigham and Women’s Hospital in Boston, randomized more than 21,000 adults to take either a daily capsule containing 500 milligrams of cocoa flavanols or a placebo for about 3.6 years. The flavanol group showed a 10 percent reduction in total cardiovascular events, a figure that fell short of statistical significance, and a 27 percent reduction in deaths from cardiovascular disease, according to the hospital.
“When we look at the totality of evidence for both the primary and secondary cardiovascular endpoints in COSMOS, we see promising signals that a cocoa flavanol supplement may reduce important cardiovascular events, including death from cardiovascular disease,” Sesso said in a statement.
“COSMOS was not a chocolate trial — rather, it’s a rigorous trial of a cocoa extract supplement that contains levels of cocoa flavanols that a person could never realistically consume from chocolate without adding excessive calories, fat, and sugar to their diet,” Manson said. “Although our study suggests intriguing signals for cardiovascular protection with cocoa flavanols, any health benefits due to taking these supplements will need confirmation in a future trial,” she added.
Much of the scientific interest in these compounds centers on the endothelium, the thin lining of the blood vessels that releases nitric oxide to help arteries relax and widen. Oxidative stress, which builds when free radicals outpace the body’s own antioxidant defenses, can wear on that lining over the years and leave vessels stiffer and more receptive to plaque. Researchers writing in Nutrients in 2013 described impaired nitric oxide-dependent vasorelaxation as “a well-established risk factor that can predispose individuals to cardiovascular disease,” and polyphenols, the family of plant compounds found in berries, tea, cocoa, and grapes, have drawn steady study for their potential to help protect it. Cardiovascular disease killed 919,032 people in the United States in 2023, about one in every three deaths, according to the Centers for Disease Control and Prevention.
What grape seed extract research shows about blood pressure
Grape seeds are rich in proanthocyanidins and carry a body of research of their own. A 2016 meta-analysis published in the journal Medicine pooled 16 randomized controlled trials with 810 participants and found that grape seed extract lowered systolic blood pressure by an average of 6.08 mm Hg and diastolic pressure by 2.8 mm Hg, with the clearest benefits among people under 50, people with obesity, and those with metabolic syndrome. A 2022 review cited by the National Center for Complementary and Integrative Health found a drop in diastolic pressure but not systolic, and the agency notes that little is known about the extract’s safety during pregnancy or breastfeeding.
WebMD’s natural medicines database rates grape seed extract as possibly effective for easing the tired, heavy legs of chronic venous insufficiency, while cautioning that grape extract might slow blood clotting. It advises stopping at least two weeks before a scheduled surgery, and anyone taking blood-thinning medication has good reason to talk with a doctor before adding it.
How polyphenol-rich foods support heart health
Ana Rodriguez-Mateos, a professor of human nutrition at King’s College London, has approached the question from the kitchen. Her team followed more than 3,100 adults in the TwinsUK cohort for over a decade and found that people whose diets leaned on polyphenol-rich foods such as tea, coffee, berries, olive oil, nuts, and whole grains had lower predicted cardiovascular risk along with healthier blood pressure and cholesterol, according to findings published in BMC Medicine in November 2025.
“Long-term adherence to polyphenol-rich diets can substantially slow the rise in cardiovascular risk as people age,” Rodriguez-Mateos said. “Even small, sustained shifts towards foods like berries, tea, coffee, nuts, and whole grains may help protect the heart over time.”
“There’s really no supplement that can prevent heart disease at the present time,” M. Hassan Murad, a preventive medicine specialist at Mayo Clinic, told the Mayo Clinic News Network. Among all the dietary interventions his team studied, reducing salt proved the most effective at lowering heart disease risk, for people with normal and high blood pressure alike.
“The manufacturers do a good job selling the idea that they can be helpful,” Leslie Cho, a preventive cardiologist at Cleveland Clinic, told the clinic’s Health Essentials, “but so-called heart health supplements aren’t tested for efficacy.”
“Don’t take chances with your heart, and make sure to run anything by your doctor that you plan to put into your body,” Cho said.
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