Vitamin D, fish oil supplements don't benefit cardiovascular health, new study finds

For decades, doctors have been searching for a surefire way to prevent atrial fibrillation, an abnormal heart rhythm that can prove fatal. Now, a new, high-quality study has ruled out two possible contenders: vitamin D and fish oil supplements.

The trial, called VITAL-Rhythm, took center stage at a recent virtual conference of the American Heart Association (AHA), the nation's largest professional organization of doctors who focus on the heart and cardiovascular system.

"Atrial Fibrillation is a very common condition and is hard to treat," said Dr. Christine Albert, the study's lead author and chair of the Department of Cardiology in the Smidt Heart Institute at Cedars-Sinai. "There are an estimated 33 million people in the world with atrial fibrillation."

Atrial Fibrillation is not benign, she explained. If left untreated, it can lead to serious health consequences such as stroke, heart attacks, heart failure, dementia, and even death. Although early, less reliable studies hinted that vitamin D and fish oil might help, doctors said this new study shows they don't make a difference.

Doctors said it's a relief to see high-quality evidence like this, because it means they can focus on new research frontiers, and avoid prescribing unnecessary pills to their patients.

Prior studies identified a possible link between these supplements and atrial fibrillation rates, but it wasn't clear if these differences were caused by the supplements themselves, or by some other unexplained factor, such as lifestyle choices.

Albert and her research team embarked on a massive study comprised of 25,000 volunteers, who would be randomly selected to receive vitamin D, fish oil or a placebo pill.

Dr. Erin Michos, the director of women's cardiovascular health and the associate director of preventive cardiology at the Ciccarone Center for the Prevention of Cardiovascular Disease at Johns Hopkins University Medical Center, said the study received praise at this year's American Heart Association conference because it was a high-quality study that included diverse volunteers. This means that the findings are applicable regardless of race and gender.

"They studied vitamin D at 2000 IU per day compared to placebo, while simultaneously studying 840 milligrams a day of marine Omega-3s vs placebo. This was a randomized clinical trial and blinded, so participants did not know whether they were taking a supplement or placebo," Michos said.

Historically, large trials have been victim to underrepresentation and lack of diversity, making it difficult for clinicians to apply these trials to their true patient population. This study, meanwhile, represented a larger population of African Americans and women.

Michos said that the importance of having a strong representation of African Americans in this trial was critical. Many have a lower blood levels of vitamin D as a result of darker skin pigmentation, which leads to poor absorption of UVB light, which is necessary to create active vitamin D and utilize its benefits.

"I actually applaud the study investigators for their efforts in diversity in this trial," Michos said. "Twenty percent enrollment of Blacks means they were overrepresented relative to their proportion in the U.S. population."

In addition, Michos said that women are frequently underrepresented in cardiovascular trials, which usually limits doctors' understanding of whether a drug or treatment will work just as well in women as it does in men.

"However, this was not the case in VITAL- Rhythm trial," Michos said. "The VITAL trial enrolled 51% women."

In recent years, research has shown a behavioral shift among some Americans toward a rise in the consumption of supplements: an estimated 120 billion dollar industry.

But researchers say the true health benefits of supplements are often overstated.

"For the vast majority of supplements, there does not appear to be any benefit. Again, more is not better if one does not have a nutritional deficiency. Some high dose supplements can even cause harm," Michos said.

The evidence is growing that supplements do not prevent primary or repeated cardiovascular disease. Another study debut at AHA, the OMEMI trial, showed no benefit in adding marine n-3 polyunsaturated fatty acids supplements to prevent a second heart attack.

But what has been shown, repeatedly, is the benefit of diet and exercise in preventing, or at times even reversing, conditions like atrial fibrillation.

"We tend to look for the magic nutrient so we do not have to eat good food," Albert said.

Albert said the most effective prevention is maintaining a healthy weight, reducing alcohol intake to 1-2 drinks per day and maintaining a healthy blood pressure.

Michos agreed, she advised that a healthy lifestyle and dietary behaviors can prevent not only atrial fibrillation, but cardiac disease overall.

"Moderate exercise, following a healthy diet, maintaining a normal weight can decrease the risk of atrial fibrillation. I think the individuals would be better served by saving their money on supplements, which have not been shown to work, and instead focus their time and money on activities that promote a healthy lifestyle," she said.

Lily Nedda Dastmalchi, D.O., M.A., is an internal medicine resident physician at The George Washington University and a contributor to the ABC News Medical Unit.