How vitamin D and fish oil reduce heart attack, stroke and cancer risk: Long-awaited VITAL study bears first results

13 Nov 2018 --- Omega 3 fatty acids can aid in reducing the risk of heart attacks, especially among African Americans, while vitamin D can reduce cancer deaths over time. These are among the long-awaited findings of the VITamin D and OmegA-3 TriaL (VITAL) study. VITAL is the first randomized clinical trial of a general population large enough to adequately address questions surrounding the effects of vitamin D and omega 3 fatty acids derived from fish oil, in high doses, on the risk of diseases such as heart attack, stroke and cancer.

Brigham and Women's Hospital investigators leading VITAL conducted a placebo-controlled trial over the course of 5.3 years, resulting in “a treasure trove” of information on the effects of both supplements.

The team found that omega 3 fish oil reduced heart attack rates but did not affect the risk of stroke or cancer. In addition, vitamin D did not significantly affect heart attack, stroke or cancer incidence but was associated with a decrease in cancer deaths that started one to two years after participants had begun treatment.

According to the researchers, VITAL is one of only a few randomized trials on a diverse study population. The VITAL population was both racially and ethnically diverse and 20 percent of the participants were African American. The team found that the reduction of heart attack risk among those taking omega 3s was especially pronounced among African American participants, with a 77 percent reduction observed.

“We found that omega 3 supplements were associated with a dramatic reduction in risk of heart attacks among African Americans in our study. If this finding is confirmed and replicated, it may point to a very promising approach to reducing coronary risk among African Americans,” says JoAnn Manson, MD, DrPH, Chief of the Division of Preventive Medicine at the Brigham.

Supported by grants from, among others, the US National Institutes of Health, VITAL enrolled 25,871 men and women age 50 and older from across the US. Eligible participants had no history of cancer, heart attack, stroke, or other forms of cardiovascular disease at the time of enrollment.

While earlier trials have examined whether fish oil or other supplements may prevent heart attack or stroke in patients with a history of heart disease or at a very high risk of such disease, VITAL is the first large trial of omega 3 fatty acids for primary prevention. This relates topreventing the first occurrence of heart disease in a general population.

VITAL was designed to test the independent effects of vitamin D and omega 3 supplements, as well as to test for synergy between the two. Participants were divided into four groups: vitamin D (2000 IU/day of vitamin D [cholecalciferol]) plus omega 3s (1g/day of Omacor [known as Lovaza in the US]); vitamin D plus placebo omega 3s; omega 3s plus placebo vitamin D; and placebos for both.

Researchers compared those who received active omega 3s with those who received placebo. After a median of five years of treatment, 805 participants had suffered a major adverse cardiovascular event, such as a heart attack or stroke (386 in the omega 3 group and 419 in the placebo group). While these rates did not statistically differ, VITAL found a significant 28 percent reduction in risk of heart attack among participants taking the omega 3 fatty acid supplements (145 cases in the omega 3 group and 200 in the placebo group). 

This effect was greater among people who had a lower fish intake (a 40 percent reduction). No significant differences were seen for cancer outcomes. The research team also examined the effect of vitamin D on cancer rates. A total of 1,617 participants were diagnosed with cancer by the end of the study; 793 had been taking vitamin D and 824 had been taking the placebo – a non-significant difference. Rates of specific forms of cancer – including breast, prostate and colorectal cancer – did not differ significantly between groups. 

However, when the team examined rates after participants had been taking supplements for at least two years, they found that cancer deaths were significantly reduced by 25 percent among those taking vitamin D. No differences were seen for cardiovascular outcomes with vitamin D.

In addition to cardiovascular disease and cancer outcomes, VITAL will report on the effects of vitamin D and omega 3s on rates of diabetes, cognitive function, autoimmune disease, respiratory infections, depression and more in the months ahead.

“Medical and public health authorities may look at the study results and decide if clinical guidelines should be updated. In the meantime, if you're already taking one or both of these supplements, there's no clear reason to stop. If you want to consider starting, our recommendation is to talk with your healthcare provider, but this does not need to be done on an urgent basis,” Manson concludes.