The study, which will involve 20,000 participants, will be led by researchers at Brigham and Women's Hospital (BWH) in Boston.
"Vitamin D and omega-3's are two of the most promising nutrients we know of for the prevention of cancer, heart disease, stroke, and many other chronic diseases, but we need large-scale randomized trials to clarify the benefits and risks," said JoAnn Manson, MD, chief of Preventive Medicine at BWH and co-leader of the trial.
The study, which has been dubbed the VITAL trial (VITamin D and OmegA-3 TriaL), will be funded by the National Institutes of Health through the National Cancer Institute and the National Heart Lung and Blood Institute, as well as other institutes and agencies.
In search of definitive evidence
The researchers hope that, if successful, the new trial will help build evidence that vitamin D and omega-3s can help reduce the burden of chronic disease.
“There is epidemiological evidence that vitamin D and omega-3 may play a role in the prevention of disease, but larger primary prevention trials have not been conducted until now. For vitamin D, previous trials have generally tested low doses and, for omega-3s, trials have been done in high-risk populations,” said BWH in a statement.
The randomized, double-blind, placebo-controlled clinical trial – which BWH says is the largest of its kind – will test whether moderate to high doses of these supplements can help prevent colorectal, breast, prostate, and other cancers, as well as heart disease and stroke.
The trial – due to “begin soon” – will run for a period of five years and will enroll 20,000 participants throughout the United States.
Participants will include women older than 65 and men older than 60 without a prior history of cancer, heart disease, or stroke. They will be randomly assigned to take either one or both of the supplements or placebo.
"The trial will be a rich resource for answering questions about the effects of vitamin D and fish oil on myriad health conditions besides cancer and heart disease - from cognitive function to vision disorders to diabetes to bone fractures," said Julie Buring, ScD, an epidemiologist in the Division of Preventive Medicine at BWH, who will be leading the study together with Manson.
"We are hopeful that this study will provide definitive proof of the effect of these nutrients on several health outcomes," she added.
Manson said vitamin D and omega-3s “have the potential of tremendously reducing the burden of chronic disease”, but said it was important to be “cautiously optimistic”.
"We tend to forget the lessons of other nutrients – many had high hopes for vitamin E, vitamin C, beta-carotene, folic acid, selenium, and other supplements as preventive tools for many diseases, but large-scale trials didn't confirm the hoped-for benefits and even found some risks when consumed at higher levels. Let's not jump on the bandwagon to take mega-doses of these supplements before clinical trials help to clarify their role," she said.
The researchers said additional studies will look at whether these nutrients have a role in preventing a wide range of other health conditions.