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Fish is often categorized as a healthy food choice since it contains a lot of protein. Studies have found that a Mediterranean diet, which is heavy on fish, can benefit health. In a new study, however, researchers suggest that fatty fish and fish oil supplements might not be as good for you as previously believed to be. In this study, researchers found that oily fish and supplements could increase one's risk of developing prostate cancer.

In this study, researchers from the Fred Hutchinson Cancer Research Center in Seattle used data taken from the Selenium and Vitamin E Cancer Prevention Trial. The team evaluated the blood levels for omega-3 fatty acids and compared them between over 800 men with prostate cancer and 1,400 men without prostate cancer. The researchers calculated that the largest difference between the highest and the lowest amounts was 2.5 percent. The researchers found that men who ate fatty fish or took supplements were about 43 percent more like to get prostate cancer than men who did not. The risk for aggressive prostate cancer jumped to 71 percent. The risk for that non-aggressive form of prostate cancer, the risk factor was 44 percent for men who had more omega-3 fatty acids in their systems.           

"These fatty acids have been promoted as a blanket anti-chronic disease fatty acid," said lead author Theodore Brasky, a research assistant professor from the Ohio State University Comprehensive Cancer Center according to HealthDay. "But nutrition is more nuanced, as is disease occurrence. It's about time we stop talking about foods as good or bad and no gray area."

Although the researchers could not identify why fatty fish and fish oil supplements contribute to an increased risk of prostate cancer, they reasoned that omega-3 fatty acids have the potential to cause oxidative stress when consumed in high levels. Oxidative stress contributes to DNA damage and could be responsible for some cancers. This study also found a correlation and not a cause and effect, and thus, whether or not fatty fish actually leads to prostate cancer remains unknown.

"All of these studies on associations, which is what this [study] is, are hypotheses-generating because they are looking back in time," Dr. Anthony D'Amico commented. D'Amico is the chief of radiation oncology at Brigham and Women's Hospital in Boston, MA. "It's not a cause and effect." He added that the study would have to take into account variables, such as age, race, and more that could also contribute to prostate cancer risk.

The study was published in the Journal of the National Cancer Institute.