Omega-3 Fatty Acids Linked to Increase in Prostate Cancer Risk

Article date: July 17, 2013

By Stacy Simon

A study conducted by researchers at cancer centers across the US has found a link between omega-3 fatty acids and an increased risk of prostate cancer. Omega-3 fatty acids are found in fish including salmon, trout, and fresh tuna, and in fish oil supplements.

The study, published online July 10 in the Journal of the National Cancer Institute, looked at blood levels of omega-3 fatty acids in some of the men enrolled in the Selenium and Vitamin E Cancer Prevention Trial (SELECT) of more than 35,000 men over age 50 in the US, Puerto Rico, and Canada. The study did not collect information on the men’s diets. Therefore, it’s not clear whether the omega-3 fatty acids in their blood came from food or from supplements.

The analysis compared 834 men from the trial who had been diagnosed with prostate cancer to a comparison group of 1,393 men selected randomly from all 35,000 participants. The researchers expected to find a protective factor from the presence of omega-3 fatty acids in the blood. Instead, they found that those with the highest levels of omega-3 fatty acids had a 43% higher risk of developing prostate cancer, and a 71% higher chance of developing high-grade prostate cancer, which is more likely to be fatal. Previous studies found similar results.

Marji McCullough, ScD, RD, strategic director of nutritional epidemiology for the American Cancer Society, said men should discuss the risks and benefits of fish oil supplements with their health care provider before taking them. She said, “In general, it’s better to try to get nutrients from foods and eat an overall healthy diet. Moderation and variety is what it always comes back to. People don’t need to eliminate fish from their diet. A healthy, balanced diet includes different types of protein sources that favor fish, chicken, and nuts over red meat.”

Omega-3 fatty acids have long been thought to have health benefits because of their anti-inflammatory properties. Inflammation plays a role in the development and growth of some cancers. But omega-3 fatty acids also have an effect on DNA, which also affects whether someone gets cancer. It is unclear from this study why high levels of omega-3 fatty acids would increase prostate cancer risk. The authors say more study is needed to figure it out.

Supplements and prostate cancer

Supplements like fish oil are among vitamins, minerals, herbs, protein powders, botanicals, and other extracts that people sometimes take because of studies and observations that indicate they may have protective properties against cancer and other diseases. However, unlike the vitamins and minerals we get through eating food, supplements usually include isolated nutrients, often in much higher doses, and sometimes with different chemical forms. Many studies over the years have been designed to investigate whether various supplements can help fight cancer.

For example, the SELECT trial that began in 2001 was designed to find out whether vitamin E and selenium could prevent prostate cancer. The study found no benefit to taking selenium and an increased risk of prostate cancer in men who took vitamin E.

More recently, a study by researchers in New York and Chicago, and published in the July 10 issue of the Journal of the American Medical Association, found that prostate cancer patients who took soy protein supplements after having their prostate removed had no benefit in terms of cancer outcomes. Their cancer returned at the same rate as men who didn’t take the supplement. The supplement was in the form of a powdered drink mixture. Because prostate cancer is less prevalent in Asian countries that have a high level of soy consumption, many prostate cancer patients in the US have tried soy supplements in the belief that it will prevent their cancer from returning.

McCullough said it is not as simple as that. She said, “Taking supplements isn't the same as eating soy, and people in cultures who eat more soy also tend to eat more vegetables and less meat.”

Despite the studies, McCullough said soy foods and fatty fish are still good, healthy alternatives to meat, especially red meat including beef, pork, and lamb. McCullough said, “It’s probably not a good idea to go overboard with anything. Moderation and variety are key to a healthy diet.”

So far, vitamin C, folate, and other supplements have also shown no promise in preventing cancer. Studies on a variety of supplements are ongoing, but much more research is needed before researchers can offer solid advice. McCullough explains more about supplements and cancer in her Expert Voices blog post: Will a vitamin a day keep cancer away?

Citation: Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial. Published online July 10 in the Journal of the National Cancer Institute. First author: Theodore M. Brasky, PhD, Ohio State University Comprehensive Cancer Center, Columbus, Ohio.

Effect of Soy Protein Isolate Supplementation on Biochemical Recurrence of Prostate Cancer After Radical Prostatectomy: A Randomized Trial. Published in the July 10 issue of the Journal of the American Medical Association (Vol. 310, No. 2). First author: Maarten C. Bosland, DVSc, PhD, University of Illinois, Chicago.

Reviewed by: Members of the ACS Medical Content Staff