JoAnn Manson, MD, DrPH, Professor of Epidemiology at the Harvard T.H. Chan School Of Public Health, discusses the results of the VITAL study, which examined the effects of omega-3 fatty acids and vitamin D on diseases like cancer and cardiovascular disease. She explains that omega-3 fatty acids did not decrease cancer incidence or cancer-related deaths.
Vitamin D and Omega-3 Supplements for Preventing Cancer and Other Chronic Diseases
JoAnn Manson, MD, DrPH
January 17, 2019
Dr. Manson discusses the results of the recently published VITAL study that tested whether vitamin D or omega-3 supplements could be effective for primary prevention of cancer and cardiovascular disease.
Q: What are the questions that the VITAL study intended to address?
DR. MANSON: Most previous studies of these dietary supplements have been observational, and we were interested in testing, in a large-scale randomized clinical trial setting, the effects of vitamin D and omega-3 fatty acid (FA) supplements on the risks of major chronic diseases, including cancer and cardiovascular disease. We wanted to have a “usual risk” population that was representative of the general public, age 50 and older and at typical risk of cancer and cardiovascular disease. All of the participants were free of these conditions at baseline.[1,2]
Q: Could you tell us about the details of the study design?
DR. MANSON: The study included nearly 26,000 US men and women. The men were age 50 and older and the women were 55 and older, with racial and ethnic diversity. As I mentioned, the participants were free of cardiovascular disease and cancer at baseline. The duration of the trial was a median of 5.3 years, so this trial was longer than many of the previous randomized trials with these supplements. We used what is called a factorial design, which enabled us to look at the independent and joint effects of the two dietary supplements. Vitamin D was given at a dose of 2,000 international units (IUs), and the omega-3 FAs (which were in the form of a prescription medication called Lovaza in the United States) had 1 gram a day of the marine omega-3 FAs EPA [eicosapentaenoic acid] and DHA [docosahexaenoic acid].
Q: What were the major results? Were any of the findings particularly surprising?
DR. MANSON: The main results of the trial focused on the primary prespecified endpoints, which were total cancer incidence and major cardiovascular events (a composite of myocardial infarction, stroke, and cardiovascular mortality). There was not a significant reduction with either of the agents. With the omega-3 FAs, there were some promising findings for myocardial infarction. For vitamin D, we saw no significant reduction in total cancer incidence, but we did see a signal for a reduction in cancer death. During the overall treatment period of 5.3 years, we saw a statistically non-significant 17% reduction in cancer death, with a hazard ratio of 0.83. However, we had planned to account for a latency period by doing some analyses that excluded early follow-up. In an analysis that excluded the first 2 years of follow-up, we did see a signal for a reduction in cancer deaths that was statistically significant, a 25% reduction, as well as a non-significant 6% reduction in cancer incidence with vitamin D. And why might there be a reduction in cancer death but not cancer incidence?
