Omega-3 fatty acids are best known for their variety of potential health benefits. However, as with many other nutrients, consuming high doses can be detrimental, potentially causing problems such as altered immune function and increased risk for prostate cancer. To avoid these risks, you can choose dietary omega-3s and limit your supplement intake to a safe level.
Higher Doses Don't Equal More Protection
Fish oil is a supplemental form of omega-3 fatty acids used to treat many conditions, including high triglycerides. According to MedlinePlus, fish oil can also be effective for reducing risk for heart disease. Howard LeWine, M.D., chief medical editor of Internet Publishing at Harvard Health Publications, notes that even though deficiencies in omega-3s have been linked to cancer, mood disorders, arthritis and other health problems, this does not mean that higher doses translate into greater protection against disease.
Prostate Cancer and Immune Alterations
High levels of fish oil have been linked to prostate cancer, according to a 2014 news article on the U.S. Department of Health and Human Services website. A study published in 2013 in "Journal of the National Cancer Institute" found that omega-3s were correlated with a 43 percent increase in overall prostate cancer risk and a 71 percent increase in aggressive prostate cancer risk. The HHS article notes that this confirms the findings of prior studies. This effect could be due in part to an increase in oxidative stress -- damage to the body caused by free radicals, which can increase the risk for cancer -- that could be caused by high levels of omega-3 fatty acids. According to a 2013 article published on the Oregon State University website, excess omega-3 fatty acids can also alter immune function, which can lead to a diminished response to infection.
Sources: Supplements vs. Food
All of the conflicting information on omega-3s can leave some people confused, to say the least. LeWine, however says you should still consider fish and seafood, rich in omega-3 fats, as healthy foods. This is because, unlike supplements, whole foods contain a combination of nutrients -- including vitamins, minerals, omega-3s and other molecules -- that work together. Other whole foods that contain omega-3s include flaxseed, flaxseed oil, walnuts, chia seeds and canola oil. The American Heart Association recommends eating fish two times per week to get your omega-3s. Norman Hord, associate professor at Oregon State's College of Public Health and Human Services, is not against using fish oil supplements, although he does note that, as with all nutrients, there are risks in taking large amounts.
Supplemental Dosage Recommendations
If you do decide to take omega-3 supplements, it is important to use a safe dose. MedlinePlus notes that fish oil is likely safe when taken in doses of 3 grams per day or less. More than 3 grams per day can interfere with blood clotting and increase your risk for bleeding. When consuming omega-3s through dietary sources, you should avoid certain fish due to their potential contamination with mercury and other chemicals. These include shark, king mackerel and farm-raised salmon.