CORVALLIS, Ore. - A new review suggests that omega-3 fatty acids taken in excess could have unintended health consequences in certain situations, and that dietary standards based on the best available evidence need to be established.
"What looked like a slam dunk a few years ago may not be as clear cut as we thought," said Norman Hord, associate professor in OSU's College of Public Health and Human Sciences and a coauthor on the paper.
"We are seeing the potential for negative effects at really high levels of omega-3 fatty acid consumption. Because we lack valid biomarkers for exposure and knowledge of who might be at risk if consuming excessive amounts, it isn't possible to determine an upper limit at this time."
Previous research led by Michigan State University's Jenifer Fenton and her collaborators found that feeding mice large amounts of dietary omega-3 fatty acids led to increased risk of colitis and immune alteration. Those results were published in Cancer Research in 2010.
As a follow-up, in the current issue of the journal Prostaglandins, Leukotrienes & Essential Fatty Acids,Fenton and her co-authors, including Hord, reviewed the literature and discuss the potential adverse health outcomes that could result from excess consumption of omega-3 fatty acids.
Studies have shown that omega-3s, also known as long chain polyunsaturated fatty acids (LCPUFAs), are associated with lower risk of sudden cardiac death and other cardiovascular disease outcomes.
"We were inspired to review the literature based on our findings after recent publications showed increased risk of advanced prostate cancer and atrial fibrillation in those with high blood levels of LCPUFAs," Fenton said.
Omega-3 fatty acids have anti-inflammatory properties, which is one of the reasons they can be beneficial to heart health and inflammatory issues. However, the researchers said excess amounts of omega-3 fatty acids can alter immune function sometimes in ways that may lead to a dysfunctional immune response to a viral or bacterial infection.
"The dysfunctional immune response to excessive omega-3 fatty acid consumption can affect the body's ability to fight microbial pathogens, like bacteria," Hord said.
Generally, the researchers point out that the amounts of fish oil used in most studies are typically above what one could consume from foods or usual dosage of a dietary supplement. However, an increasing amount of products, such as eggs, bread, butters, oils and orange juice, are being "fortified" with omega-3s. Hord said this fortified food, coupled with fish oil supplement use, increases the potential for consuming these high levels.
"Overall, we support the dietary recommendations from the American Heart Association to eat fish, particularly fatty fish like salmon, mackerel, lake trout or sardines, at least two times a week, and for those at risk of coronary artery disease to talk to their doctor about supplements," he said.
"Our main concern here is the hyper-supplemented individual, who may be taking high-dose omega-3 supplements and eating four to five omega-3-enriched foods per day," Hord added. "This could potentially get someone to an excessive amount. As our paper indicates, there may be subgroups of those who may be at risk from consuming excess amounts of these fatty acids."
Hord said there are no evidence-based standards for omega-3 intake and no way to tell who might be at health risk if they consume too high a level of these fatty acids.
"We're not against using fish oil supplements appropriately, but there is a potential for risk," Hord said. "As is all true with any nutrient, taking too much can have negative effects. We need to establish clear biomarkers through clinical trials. This is necessary in order for us to know who is eating adequate amounts of these nutrients and who may be deficient or eating too much.
"Until we establish valid biomarkers of omega-3 exposure, making good evidence-based dietary recommendations across potential dietary exposure ranges will not be possible."
Sanjoy Ghosh from University of BC-Okanagan, Canada and Eric Gurzell from Michigan State University also contributed to this study, which was supported by grants from the National Institutes of Health and the Canadian Diabetes Association.
If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.
Just because fish oil supplements are good for you doesn’t mean more is even better. Side effects like indigestion, heartburn, and bad breath typically show up on high doses of these supplements. Let’s look at how much fish oil is too much and what side effects to look out for.
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When we talk about fish oil, we’re referring to omega-3 fatty acids that you get from supplements or eating fish. You’ll find omega-3s in fatty fish like mackerel, salmon, sardines, herring, tuna, and cod liver, as well as fish oil capsules found at your local drug store.
There are different types of omega-3 fatty acids, but two of the most important ones are called eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). They might be a mouthful, but these polyunsaturated fatty acids can help with all types of health issues like preventing and even reversing heart disease (Novotny, 2022).
If you follow a vegan or vegetarian diet, you can get what’s called alpha-linolenic acid (AHA), a type of omega-3 derived from algae or flaxseed oil.
It’s worth noting that fish oil is generally well-tolerated. Even though fish oil supplements have health benefits like reducing inflammation and lowering blood pressure, taking too much can have adverse effects. Most people experience side effects on high doses of fish oil, while others may notice them taking lower amounts. Let’s look into some of the more common side effects.
Sometimes the taste of fish oil supplements is hard to swallow, even for fish lovers. Vitamin burps don’t just happen with fish oil and can be a sign that whatever you took is breaking open before it hits your digestive tract.
Most of this is anecdotal, but many people report belching, fishy breath, and unpleasant-smelling sweat when taking fish oil. While storing your supplements in the fridge can lessen or dull the fishy flavor, it may not prevent the smell from sweating out during a workout.
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Digestive issues are some of the most common side effects of omega-3 supplements, specifically indigestion, heartburn, diarrhea, nausea, and flatulence. Depending on the type of omega-3 fatty acids you take, other side effects you may notice include constipation, taste changes, and vomiting (Novotny, 2022; Khodarahmi, 2016).
Vegans looking to get their omega-3s through algae or flaxseed oil aren’t immune from similar side effects. In fact, flaxseed oil may increase bowel movements enough to make it a viable treatment for constipation (Ramos, 2015).
Despite what you might think, it’s rare for people allergic to fish or shellfish to also have an allergy to pure fish oil. However, if you have known fish or shellfish allergies, you may want to consider using flaxseed or algae oil as an alternative. You can also discuss the risks with your healthcare provider (Novotny, 2022).
There are other purported side effects of fish oil, but there simply isn’t enough research to support them as fact. Here are other adverse effects claimed by some, although again, the scientific evidence on this is limited:
- Increased risk of bleeding, especially when taking anticoagulants (blood thinners)
- Bleeding in the stomach or intestines (ulcers)
- Stroke
- Vitamin A toxicity
- Insomnia
- Higher risk of prostate cancer
- Low blood pressure
Interestingly, the ability of fish oil to lower blood pressure is one of its many health benefits. That said, there is a chance that this could be dangerous for people who don’t have high blood pressure.
According to the Office of Dietary Supplements (ODS), the recommended daily intake of omega-3 fatty acids is 1,100 mg for women and 1,600 mg for men (OSD, 2021).
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Many people take fish oil supplements because of the potential health benefits. Some common uses and conditions fish oil may help with include (Novotny, 2022; OSD, 2021):
- High triglyceride (cholesterol) levels
- Heart disease
- Inflammatory conditions like rheumatoid arthritis
- Depression
- Cancer prevention
- Dry eye
- Alzheimer’s disease
- Age-related macular degeneration (AMD)
- Promoting maternal and fetal health during pregnancy
Taking the recommended dose of fish oil is not likely to cause serious side effects. Know that if you start taking higher doses, you’ll see more side effects than if when staying within the recommended range. Your healthcare provider can give you medical advice regarding the risks and benefits of fish oil supplementation.
- Khodarahmi, M. & Azadbakht, L. (2016). Dietary fat intake and functional dyspepsia. Advanced Biomedical Research, 5, 76. doi:10.4103/2277-9175.180988. Retrieved from //www.ncbi.nlm.nih.gov/pmc/articles/PMC4863403/
- Novotny, K., Fritz, K., & Parmar, M. (2022). Omega-3 fatty acids. [Updated Jan 6, 2022]. In: StatPearls [Internet]. Retrieved Feb. 8, 2022 from //www.ncbi.nlm.nih.gov/books/NBK564314/
- Office of Dietary Supplements (OSD). (2021). Omega-3 fatty acids. Retrieved Feb. 8, 2022 from //ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/
- Ramos, C. I., Lima, A. F. A. D., Grilli, D. G., & Cuppari, L. (2015). The Short-Term Effects of Olive Oil and Flaxseed Oil for the Treatment of Constipation in Hemodialysis Patients. Journal of Renal Nutrition, 25(1), 50–56. doi:10.1053/j.jrn.2014.07.009. Retrieved from //pubmed.ncbi.nlm.nih.gov/25238699/