What is the COSMOS study?

The term COSMOS is derived from “COcoa Supplement and Multivitamin Outcomes Study.” The COSMOS Study is a large-scale, placebo-controlled, clinical trial testing the risks and benefits of supplemental cocoa extract and a multivitamin in the primary prevention of cancer and cardiovascular disease. The primary outcomes of the study are heart attack, stroke, coronary revascularization, cancer and death.


Who is running the COSMOS study?

COSMOS is run by Brigham and Women’s Hospital, an affiliate of Harvard Medical School, in Boston, MA, and the Fred Hutchinson Cancer Research Center in Seattle, WA.


How is the COSMOS study supported?

COSMOS represents an important partnership across academic, industry, and government collaborators. COSMOS is supported by an investigator-initiated grant from Mars Symbioscience and the donation of study pills and packaging from both Mars Symbioscience and Pfizer Inc (now part of GSK Consumer Healthcare). In addition, COSMOS ancillary studies are supported by several grants from the National Institutes of Health.


Who is participating in the COSMOS study?

Women aged 65 or older and men aged 60 or older who have not previously had a heart attack or stroke, or cancer (other than skin cancer) diagnosed within the last two years are participating in the COSMOS study. Participants live in every state in the U.S., with study pills sent via postal mail and study forms completed either through the web or by postal mail.

Map of participants' residence (all 50 states)


What does participation involve, now that COSMOS pill-taking has ended?

Even though the pill taking phase has now concluded, the COSMOS Study will continue! COSMOS participants are still part of an incredibly unique large-scale scientific endeavor to understand not only the long-term health effects of the randomized cocoa extract and multivitamin interventions, but also to deepen our understanding of healthy aging. We expect to continue to send questionnaires to COSMOS participants, as well as provide opportunities for involvement in other important substudies and new research studies. Questionnaires received completed on the web or via postal mail will take approximately 15-20 minutes to complete, with questions about health; lifestyle habits such as exercise, diet, and smoking; use of medications and dietary supplements; and family history of illness. Occasionally, participants are contacted by phone to collect information or to clarify questionnaire responses.


What was the likelihood that I was assigned to at least one “real” study supplement, rather than a placebo?

All participants had an equal chance of being assigned to one of the four study groups: (1) daily cocoa extract and multivitamin (25% chance); (2) daily cocoa extract and multivitamin placebo (25% chance); (3) daily cocoa extract placebo and multivitamin (25% chance); or (4) daily cocoa extract placebo and multivitamin placebo (25% chance). There is therefore a 25+25+25=75% chance that you were taking at least one “real” supplement.


Can I get the same amount of cocoa flavanols from chocolate as the amount in the active cocoa extract capsules?

It would be very difficult to get this amount of cocoa flavanols from chocolate without adding a large number of calories. See the chart below:


Will my health information be kept confidential?

Yes! We are committed to protecting your privacy. Information from completed questionnaires and medical records is identified in our computer files by study number only, and only a few staff members, who have received training in—and understand the importance of—protecting confidential health information, have access to the file that links study numbers with participants’ names. Your information will be used only for COSMOS, and no personal information will identify participants in published research findings. Your trust is essential to the success of the study, and we would never do anything to risk losing your faith in us.


What was the reason for collecting blood and urine samples from participants?

As an optional part of COSMOS, we requested blood and urine samples from willing participants selected at the start of the study. These samples will allow us to study whether baseline blood levels of cocoa flavanols, other pertinent nutritional biomarkers (chemicals), and vascular/metabolic biomarkers are related to (a) an individual’s risk for developing a particular disease and (b) the effects of cocoa extract or multivitamin supplements on pathways relevant to major health conditions. Interested study participants received a blood and urine kit, including collection instructions, in the postal mail. Some participants were able to have their blood drawn by their local healthcare providers, whereas others required assistance in locating someone to draw their blood.


May I have a copy of my blood test results? If not, why?

Unfortunately, we do not release the results of blood tests to study participants. There are four reasons for this policy. First, we will not analyze the blood samples until the end of the study, so the results will not be an accurate measure of flavonoids and other biomarker levels at that time. Second, some lab tests will be done on only a sample of participants (not on everyone). Third, the labs we will use to analyze the blood samples are certified as research labs rather than clinical labs—this means that they apply different standards for analysis and their results cannot be directly compared with results from clinical labs. Fourth, informing participants of blood test results could bias the study’s findings if a large percentage of participants start to take cocoa flavanol supplements on their own to achieve a blood level that they think is best (COSMOS is designed to test this very question—i.e., does a higher blood level of flavonoids actually provide health benefits compared with an “average” blood level?).


I’ve recently moved into a new home. How can I ensure that I will continue to receive mailings in a timely fashion?

To ensure that study mailings continue without delay, please notify us of changes in your mailing address, phone number, and e-mail as soon as possible (1-800-633-6913 or, and please inform us of the start date for these changes. If it is only a part-time residence (such as moving to a different location for the winter), please provide the expected dates and duration of time you will be at this 2nd location.


Why do you ask for date of birth on every questionnaire?

In a study as large as COSMOS, there are often one or more participants with the same name. In addition to your name and study ID number, your date of birth serves as a unique identifier.


Why do you ask for the name and number of a contact person?

In a long-term study such as COSMOS, we occasionally lose touch with study participants when they move or have other changes in their status. We may write or call your contact person to ask for your current address or phone number only if we cannot reach you after multiple attempts.


My doctor wants to know what study pills I was taking as part of the COSMOS study. What should I tell them?

Please tell your doctor that you were taking part in a 4-year randomized clinical trial of cocoa extract (containing 600 mg per day of cocoa flavanols) and a multivitamin for the prevention of cardiovascular disease and cancer. Your orange study capsules contained either 600 mg of cocoa extract or placebo, and your grey study tablet contained either a multivitamin or placebo. At the end of the pill taking phase of the trial, you will be told which type of study agents you were taking. Although it may be helpful for your doctor to be aware of your participation in COSMOS, neither you nor your doctor should assume that the study capsules can replace any of your prescribed medications.


I am aware that all dietary supplements, including cocoa extract and multivitamins, have possible benefits and possible risks. Are the data monitored regularly to be sure that participants are not experiencing undue risks from participating in the study?

Cocoa extract and multivitamins, in the doses that COSMOS is testing, are among the safest of dietary supplements. Participant safety is of the highest priority to COSMOS investigators. Indeed, in clinical trials, keeping a close eye on all health outcome data to check for safety concerns is required by the National Institutes of Health. All health outcome data collected in COSMOS are carefully reviewed at least once per year by a panel of outside medical and statistical experts who are not affiliated with the study. This panel is called the Data and Safety Monitoring Board. If an unacceptably high risk for the cocoa extract supplement or the multivitamin were to be found, that part of the trial would be stopped and participants would be notified as soon as possible.