Taking vitamin D and omega-3 fatty acids could prevent cancer and heart attacks, according to a study that adds to the debate around the benefits of supplements.
The study involved 25,871 people in the U.S. who took part in the Vitamin D and Omega-3 Trial (Vital) clinical trial for five years. Some participants took only vitamin D or fish oil; others took both; and some acted as the control by consuming neither supplement.
The findings showed that taking vitamin D was linked with a lower risk of dying of cancer in people of a normal weight—or a BMI of 18.5 to 25 on average.
Omega-3 fatty acids were meanwhile linked to a lower risk of heart attacks. On average the participants ate an average of 1.5 servings of fish per week, and those who ate less than the average appeared to benefit most from the supplement.
The findings were presented at the 30th Annual Meeting of The North American Menopause Society (NAMS), and have not been published in a peer-reviewed journal.
JoAnn Manson, lead author of the study and an epidemiologist at Harvard's Brigham and Women's Hospital, cautioned that the findings suggest a "complex balance of benefits and risks" for taking either vitamin D or omega 3 supplements.
Stephanie Faubion, medical director of NAMS who did not work on the study, commented in a statement: "With heart disease and cancer representing the most significant health threats to women, it is imperative that we continue to study the viability of options that prevent these diseases and help women survive them."
Health benefits of supplements: An ongoing debate
The findings add to the debate on how well eating omega 3-fatty acid supplements protects our health. Last year, a separate team concluded eating fish oil didn't lower a person's risk of dying of any cause, including heart attack and stroke. The study involved more than 112,000 participants.
Omega-3 fatty acids are an essential fat that the body can't make itself. Foods such as fish, vegetable oils, walnuts and other nuts, flaxseeds, and leafy vegetables contain the nutrient which helps the body making certain hormones related to inflammation, the blood and heart.
Over the past 15 years conflicting evidence has emerged on whether taking fish oil supplements containing omega-3 fatty acids is beneficial. The American Heart Association stated in 2017 that most people don't need fish oil supplements—although they aren't a risk to health. The oils may lower the risk of dying after heart failure or a recent heart attack, the organization said, but don't appear to prevent heart disease.
Kris-Etherton Penny Kris-Etherton, a nutrition professor at Penn State University who co-authored the advisory, commented at the time: "People are not getting enough omega-3 fatty acids. Of course, people should eat fish first, but if they can't meet those recommendations with fish, fortified foods or supplements are OK."
Vitamin D, meanwhile, helps the body absorb and retain calcium and phosphorus, which help it to build bone. Some 1 billion people are believed to have vitamin D deficiency, with those who live north of the horizontal line—linking San Francisco to Beijing—most at risk. Being in the sun causes the body to create vitamin D, and it can also be consumed in fatty fish like salmon and tuna, as well as foods manufactured to contain the nutrient.
Commenting broadly on the topic Katie Patrick, the health information officer at the charity Cancer Research U.K., who did not work on the study, told Newsweek: "No one food or supplement is more important than having a healthy and balanced diet overall.
"So far the evidence says that vitamin D and fish oil supplements don't help prevent cancer developing. But studies have found signs that vitamin D may help reduce the risk of dying from cancer. However it's too early to jump to any real conclusions as the evidence has been mixed so far.
"Consider taking vitamin D supplements over the winter, and groups at risk of low vitamin D levels—like young children, people with dark skin and the elderly—are recommended to take it all the time."
Victoria Taylor, senior dietitian at the charity the British Heart Foundation, told Newsweek: "Fish—white and oily—is a nutritious choice and it's recommended that we eat two portions per week, one of which is oily.
"Eating more fish is consistent with the Mediterranean-style diet and research into this style of eating has shown a reduced risk of developing problems such as type 2 diabetes, high blood pressure and raised cholesterol, which are all risk factors for heart disease."