Drinking flavanol-rich cocoa three times a day improved walking distance in individuals with peripheral artery disease (PAD), reports a new Northwestern Medicine pilot study. The disease affects about 8.5 million people in the U.S.
People with PAD have blockages in their arteries that slow or stop the blood flood flow to their legs. As a result, they have pain and difficulty walking even short distances.
“The degree of improvement from chocolate was significant and meaningful,” said lead author Dr. Mary McDermott, the Jeremiah Stamler Professor of Medicine at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician. “Exercise currently is the most effective medical therapy for PAD. In this study, the benefits from chocolate were comparable to the benefits of exercise.”
McDermott stressed the trial of 44 people was a small sample size, and a larger clinical trial is needed to confirm the findings.
The study was published Feb. 14 in Circulation Research.
People 60 years and older who drank the cocoa beverage three times a day for six months were able to walk up to 42.6 meters or about 140 feet farther in a six-minute walking test, compared to those who drank the same type of beverages without cocoa.
Participants had their blood flow measured in their legs using magnetic resonance imaging. Those who consented had a calf muscle biopsy to evaluate muscle health.
The cocoa used in the study was rich in epicatechin, which exists in larger quantities in dark chocolate (more than 85% cacao) than in milk chocolate. The flavanols with epicatechin also are available in a pill, which reduces the risk of weight gain from drinking cocoa three times a day.
With aging, blood flow to the legs declines even in otherwise healthy people. Older people also have poorer muscle health and mitochondrial activity. Therefore, although not tested in this study, there is the potential for cocoa to help improve walking in older people without PAD as well, McDermott said.
McDermott, who enjoys half a bar of dark chocolate most days, said that it was reasonable for people with PAD to consume a small amount of dark chocolate on a daily basis.
Participants in the cocoa group of the trial drank a beverage containing one tablespoon of unprocessed, non-alkalized cocoa three times daily. That’s a total of 75 milligrams of epicatechin, the most prominent flavanol in cocoa, believed to be responsible for the improvement in blood flow and walking. Flavanols are a type of antioxidant made by plants and are present in some fruits, vegetables and cocoa.
(Alkalized or Dutch-process cocoa powder is washed with a solution that neutralizes cocoa's acidity. This process destroys the flavanols.)
Researchers found the cocoa drinkers had 20% improved blood flow to their calves and improved muscle health and function compared to the placebo group. The cocoa drinkers also had 14% increased density of their capillaries, tiny blood vessels that deliver oxygen to the tissue. The improvement in capillaries has been shown in animal studies; this is the first time it has been shown in humans.
In addition, mitochondrial activity, a marker of energy production in the cell and healthy muscle, improved 98%. The cocoa reached its peak effect three hours after ingestion.
A treadmill test did not show an improvement in walking distance, but McDermott said the improvement in six-minute distance walking better reflects the walking required in daily life and is a more relevant outcome for patients with PAD.
“The epicatechins in chocolate help dilate blood vessels, which enables more oxygen to travel to the tissues,” McDermott said. “In animal studies, epicatechin also promotes muscle growth and can reverse the atrophy of muscles common in PAD patients.”
Patients who drank the placebo beverage had a decline in their walking distance compared to their baseline results, which is typical of other studies in which people with PAD without treatment have declines in their six-minute walking distance over time.
"This is a painful, disabling disease," McDermott said. “If these findings are confirmed in a larger study, cocoa, a relatively inexpensive, safe and accessible product, could potentially produce significant improvements in calf muscle health, blood flow and ultimately walking for PAD patients.”
Other Northwestern authors include Kathryn Domanchuk, Dr. Donald Lloyd-Jones, Linda Van Horn, Dongxue Zhang and Lihui Zhao.
The study was funded by grant R21-AG05087 from the National Institute on Aging, the intramural office of the National Institute on Aging and the Office of Dietary Supplements of the National Institutes of Health. The cocoa beverage and matching placebo were provided by The Hershey Company.