A large U.S. study known as VITAL, conducted in healthy adults, concluded that omega-3 supplements can dramatically reduce the odds of a heart attack while vitamin D may lower the the risk of death from cancer.
Neither vitamin D (2000 IU/day) nor fish oil (1 gram/day) lowered the risk of stroke or of developing cancer in the first place.
About the study
The trial, which ran for 5.3 years, enrolled 25,871 Americans of various ethnicities who were over the age of 50 and had no previous history of cancer, heart disease or stroke.
Participants were randomly assigned to take either 2000 IU (international units) of vitamin D3 and one gram of omega-3 fatty acids from fish oil, a vitamin D and a placebo pill in lieu of fish oil, or a fish oil supplement and a vitamin D placebo pill.
The findings: Compared to the placebo group, vitamin D supplementation did not lower the risk of cancer (total cancers or breast, prostate or colorectal cancers) or major cardiovascular events (defined as a composite of heart attack, stroke and death from cardiovascular disease).
Likewise, participants taking a daily omega-3 fatty acid supplement did not experience a reduction in cancer or major cardiovascular events compared to the placebo group.
Fish oil and heart attack risk
When the researchers looked at heart attacks specifically, they found that participants taking the omega-3 supplement had a 28 per cent lower heart attack risk and a 50 per cent reduced risk of fatal heart attack compared to the placebo group.
Among participants who ate less than 3 to 4 ounces of fish per week, supplementing with fish oil led to a 19 per cent reduction in major cardiovascular events, including a 40 per cent lower risk of heart attack, compared to the placebo group.
People who ate at least two servings of fish per week did not benefit from taking a fish oil, perhaps because they were already getting adequate omega-3’s by eating fish.
Among African Americans, taking fish oil led to a 77 per cent reduction in heart attacks, whether these participants were low fish eaters or not.
Vitamin D and cancer deaths
For people taking vitamin D who developed cancer, the death rate from cancer was 25 percent lower, possibly because the vitamin “may affect the biology of the tumor so it’s less likely to spread and become metastatic,” said lead author from Brigham and Women’s Hospital in Boston.
People should not take higher doses than what was used in the study, the researchers noted. With very high doses, the risk may outweigh the benefit.
Sources: The New England Journal of Medicine, online November 10, 2018.
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