Can cocoa flavanols prevent disease?

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Rebekah Alcalde

Chocolate lovers may be on to something. A new long-term study is trying to find out if taking daily, dietary supplements of cocoa extract containing cocoa flavanols and theobromine from the cocoa bean, and/or a standard multivitamin reduces the risk of developing cardiovascular disease and cancer.

The study is being conducted in a partnership by Brigham and Women’s Hospital and the Fred Hutchinson Cancer Research Center in Seattle, Wash., and volunteers are being recruited nationwide.

The study, called COSMOS, “is the largest and longest duration dietary intervention trial to date that will investigate the impact of cocoa flavanols on risk of heart attack, stroke and death from cardiovascular disease,” explained lead investigator Dr. JoAnn Manson, who is also chief of the division of preventative medicine at the hospital. They will also be testing multivitamins to see if they have similar effects.

This national trial is conducted primarily by mail and can be done remotely. They plan to enroll 18,000 participants nationwide to participate in the study for four years.

Studies indicate benefit

Cocoa is a fermented product made from the bean of the cocoa tree, and preliminary research suggests it can have a powerful impact on your health.

Small randomized trials have demonstrated promising benefits for cocoa flavanols, including improving blood pressure, lipid (cholesterol) levels, and the body’s insulin sensitivity, which decreases the chance of getting Type 2 Diabetes.

For multivitamins, a prior large-scale randomized trial in middle-aged and older men showed a significant reduction in cancer, but comparable trial data in women are lacking.

For both products, a large-scale clinical trial such as COSMOS could have major clinical and public health implications.

Additionally, COSMOS will examine how cocoa flavanols affect brain health. Smaller studies from Columbia University Medical Center and the University of L’Aquila in Italy “indicate that cocoa flavanols may help with multiple aspects of cognitive health and function, including slowing the rate of age-related memory loss in healthy individuals,” Manson said.

Over the course of the trial, approximately 4,000 participants will be asked to complete four web-based assessments of their cognitive functioning, which each take about 25 minutes to complete.

Getting involved

Interested individuals first complete questionnaires that will determine if they are eligible to participate, together with an informed consent form. The questionnaires ask about health, lifestyle habits (such as exercise, diet, smoking), use of medications and dietary supplements, and family history of illness.

Those individuals invited to participate in the study will be randomly assigned to one of four groups: (1) daily cocoa extract and multivitamin; (2) daily cocoa extract and multivitamin placebo; (3) daily cocoa extract placebo and multivitamin; or (4) daily cocoa extract placebo and multivitamin placebo. A placebo looks exactly like the study supplement, but it contains no active ingredients.

No matter which group a participant is assigned to, she or he will take three pills each day — two capsules that contain either cocoa extract or cocoa extract placebo, and one tablet that contains either a multivitamin or multivitamin placebo. Participants will receive their study pills in convenient calendar packages via postal mail.

Each year that a participant is in the research study, she or he will receive a mailed questionnaire that takes approximately 15 to 20 minutes to complete. These forms are similar to the original eligibility forms. Occasionally, participants will be contacted by phone to collect information or to clarify questionnaire responses.

Eligibility and requirements

Eligible participants include women who are 65 and older and men 60 and older, who have not had a heart attack, stroke or cancer diagnosed in the past two years (excluding skin cancer), or any major illness that would affect the study.

Participants must also have no history of myocardial infarction or stroke, any extreme sensitivity to caffeine — since cocoa naturally contains caffeine — or be unable to communicate in English due to language barrier or mental incapacity.

During the study, they must also forgo personal use of multivitamins and cocoa extract supplements. Also, they must limit their total intake of vitamin D (besides the study medication) from supplements to 1000 IU or less per day, and their total intake of calcium from supplements to 1200 mg. or less per day.

On the plus side, participants can still eat chocolate.

For more information, visit or call 1-800-633-6913.