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CHICAGO -- Supplementation with vitamin D or omega-3 fatty acids did not lead to a lower incidence of cardiovascular events or invasive cancer versus placebo, researchers reported here.

In the VITAL trial, 1,617 participants were diagnosed with cancer (793 taking vitamin D; 824 on placebo) during 5.3 years of follow-up (hazard ratio 0.96, 95% CI 0.88-1.06, P=0.47) reported JoAnn Manson, MD, Brigham & Women's Hospital-Harvard Medical School in Boston, and colleagues at the American Heart Association (AHA) annual meeting and simultaneously in the .

In the same VITAL population, a occurred in 386 people taking marine n-3 (omega-3) fatty acids versus 419 participants on placebo during 5.3 years of follow-up (HR 0.93, 95% CI 0.80-1.06, P=0.24)

However, Manson reported that there were secondary outcome measures that hinted at benefits for supplementation.

"Omega-3s reduced total myocardial infarction [MI] by 28% (nominal P=0.003), with greatest reductions in those with low dietary fish intake and in African Americans. Percutaneous coronary interventions, fatal MIs, and total coronary heart disease were also reduced," she said, adding that "Vitamin D reduced total cancer mortality in analyses excluding early follow-up."

Manson said that other aspects of the VITAL findings, including the impact of vitamin D on fractures, are still being analyzed. She also suggested that researchers may want to consider a trial on omega-3s impact on MI.

AHA discussant Jane Armitage, MBBS, of Oxford University in England, said that "The most robust finding from this study is that neither omega-3 fatty acids nor vitamin D significantly reduced the primary endpoints of major cardiovascular disease events or total invasive cancer," and that the secondary findings were less robust.

The VITAL trial enrolled 25,871 individuals in a 2-by-2 factorial study protocol that allowed multiple research questions to be answered in one trial.

For the omega-3 study, 12,933 individuals were assigned to the fish oil supplements and 12,938 to placebo. For the vitamin D part, 12,927 individuals were assigned to receive the study supplement and 12,944 people were given placebo.

The mean age of the participants was 67.1 and 50.6% were women. The cohort included 20.2% African-American participants.

The mean BMI was 28.1, and 7.2% were current smokers, while about half had hypertension that was being treated. Also, about 37.5% were being treated for high cholesterol, and 13.7% were diagnosed with diabetes.

The omega-3 dose was 1 g/day, while the vitamin D dose was 2,000 IU/day. Manson reported that >83% of the trial participants adhered to the study agents for 5.3 years of follow-up.

In an, John Keaney Jr., MD of the University of Massachusetts Medical School in Worcester, and Clifford Rosen, MD, of the Maine Medical Center Research Institute in Scarborough, wrote "In the absence of additional compelling data, it is prudent to conclude that the strategy of dietary supplementation with either marine n-3 fatty acids of vitamin D as protection against cardiovascular events or cancer suffers from deteriorating VITAL signs."

But they also noted that the secondary endpoints are likely to draw attention.

Manson's group wrote that "the results of subgroup analyses raise the possibility of differential effects on cancer incidence according to BMI, with normal-weight participants who received vitamin D having a lower incidence than those who received placebo." Also, "the findings in the subgroup analyses of the secondary endpoint of myocardial infarction that suggested possible greater cardiovascular benefits of n-3 supplements in blacks than in non-Hispanic whites was unexpected...it may be a chance finding that would require corroboration in future trials."

Kearney and Rosen urged caution when viewing these "positive" results, noting that these results were not seen in other large, randomized trials of n-3 fatty acids.

The trial had limitations including the inability to assess dose-response relationships for either vitamin D or omega-3.