Fish oil, which contains the omega-3 fatty acids DHA and EPA, has long been touted as beneficial for cardiovascular health, mental health (including depression and Alzheimer’s disease) and arthritis, just to name a few. 
Now, a new study is reporting that high doses of the compound can increase one’s risk of high-grade prostate cancer. Before you abstain from all fish and omega-3 consumption, let’s take a closer look.
The terms “fish oil” and “omega-3 fatty acids” are often used interchangeably, which can actually be misleading. Allow me to explain: fish and fish oil contain the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). The third omega-3 fatty acid, alpha-linolenic acid (ALA) is found in nuts and vegetable oils and can be converted, in small amounts, into DHA. Therefore, when using the term “fish oil,” you are actually only referring to two of the three omega-3’s. With that said, however, most of the evidence supporting the health benefits of omega-3’s refers to the two components of fish oil: DHA and EPA, whereas evidence supporting the health benefits of ALA is lacking.
The American Heart Association recommends consuming fish (particularly fatty fish like salmon) twice a week and the Food and Drug Administration (FDA) considers up to 3 grams of fish oil per day as “generally regarded as safe.” Consumption of more than 3 grams per day can increase your risk of bleeding and should be discussed with your doctor first.
Now to the study – researchers at the Fred Hutchinson Cancer Research Center looked at a subset of the Selenium and Vitamin E Cancer Prevention Trial (SELECT) population: 834 men who developed prostate cancer and 1,393 randomly chosen men who did not have cancer. These men were divided into four groups based on their blood levels of the three omega-3 fatty acids. The researchers found that men who have the highest levels of these compounds have a 71 percent increased risk of high-grade prostate cancer and a 43 percent increase for all prostate cancer.
The key message here is that this research did not establish a causal relationship between omega-3 fatty acid consumption and prostate cancer. Furthermore, while these statistics are indeed alarming, a few more questions need to be answered. More research is needed into why such high concentrations of omega-3 fatty acids are associated with an increased risk of prostate cancer, especially high-grade disease; we need to understand the biological mechanism behind the findings. We also need to understand how consumption of omega-3’s affect men who have already been diagnosed with prostate cancer.
Different people may have different levels of omega-3 fatty acids in their blood despite similar intake, so speak with your physician about either beginning or discontinuing these supplements or general fish consumption. If you have a heart condition or elevated cholesterol levels, speak with your cardiologist to discuss the benefits and risks of omega-3 fatty acid/fish oil supplementation before making any modifications on your own.
