Two new randomized trials challenge the view that vitamin D and fish oil supplements hold any real benefit in the fight against chronic conditions, such as cancer and heart disease.
Vitamin D and fish oil supplements have lately been the subject of much hype in the medical research community, mass media, and among the general public, due to their alleged benefits in combatting cancer and heart disease.
Experts also believe that omega-3 fatty acids — which are in seafood, some nuts, and seeds — benefit the heart. The AHA, for example, recommend an intake of at least 2 servings of fish every week for optimal cardiovascular health.
As a result, many Americans have turned to omega-3 fish oil supplements to stave off heart disease. A survey carried out by the National Institutes of Health (NIH) found that almost
But do vitamin D and fish oil supplements really work?
Vitamin D, fish oil no better than placebo
The two new studies were randomized, placebo-controlled trials led by Dr. JoAnn E. Manson, the chief of the division of preventive medicine at the Brigham and Women's Hospital in Boston, MA.
The trials examined the effect of a daily intake of vitamin D and omega-3-containing fish oils on the prevention of heart disease and cancer.
The studies involved almost 26,000 healthy adult participants, 20 percent of whom were African-American. None had a history of heart disease or cancer. The men in the study were at least 50 years old, and the women were at least 55.
Some participants took a daily dosage of 2,000 international units of vitamin D and 1 gram of fish oil.
Other participants received the same dosage of vitamin D plus a placebo, and others took the same daily dosage of fish oil with a placebo. The final group received two dosages of placebos.
Dr. Manson and the team followed the participants for 5 years. By the end of the study period, they had found no overall benefits.
In the first trial, they conclude:
"Supplementation with [omega-3] fatty acids did not result in a lower incidence of major cardiovascular events or cancer than placebo."
In the second trial, they surmise that "Supplementation with vitamin D did not result in a lower incidence of invasive cancer or cardiovascular events than placebo."
Does fish oil stave off heart attacks?
Dr. Manson and the team did find a link between fish oil and a lower risk of heart attacks, particularly among people who did not eat fish regularly, as well as among African-Americans.
Overall, fish oil supplements reduced the risk of a heart attack by approximately 28 percent. Among African-Americans, fish oil supplements lowered this risk by 77 percent, compared with participants who took only a placebo.
Finally, the researchers found that no supplement involved in the trial led to severe side effects, such as bleeding, excessive calcium, or gastrointestinal problems.
The New England Journal of Medicine also published an editorial related to the trials. In it, authors Dr. John F. Keaney and Dr. Clifford J. Rosen warn that the trials' "positive" results regarding fish oil supplementation and heart attack risk "need to be interpreted with caution."
They continue, noting that other large randomized trials of omega-3 fatty acids do not support these findings.