Health effects of fish oil

Health effects

Kepler cod liver oil with malt extract

History

Fish oil became one of the earliest dietary supplements, and by the end of the 19th century, was used as a treatment for many diseases, including such ailments as tuberculosis and hysteria.^[17][18][19] The possible effects of fish oil and omega-3 fatty acids have since been studied in clinical depression,^[20][21] anxiety,^[22] cancer, and macular degeneration, yet they have not been proven effective.^[23]

Various recommendations

In a 2009 letter on a pending revision to the Dietary Guidelines for Americans, the American Heart Association recommended 250–500 mg/day of EPA and DHA.^[24] The Guidelines were revised again for 2015–2020; included is a recommendation that adults consume at least eight ounces of a variety of types of fish per week, equating to at least 250 mg/day of EPA + DHA.^{[citation needed]} The Food and Drug Administration recommends not exceeding 3 grams per day of EPA + DHA from all sources, with no more than 2 grams per day from dietary supplements.^[25]

Prostate cancer

The effect of fish oil consumption on prostate cancer is controversial.^[26][27] For instance, one study showed decreased risk with higher blood levels of DPA. However, another reported increased risk of more aggressive prostate cancer with higher blood levels of combined EPA and DHA.^[28] Some evidence indicated an association between high blood levels of omega-3 fatty acids and an increased prostate cancer risk.^[29]

However, this evidence from the Select Trial has been challenged on the grounds of methodology and that the quantitative difference between those who developed prostate cancer and those who did not "is so small as to be biologically irrelevant".^[30]

Cardiovascular

There is uncertainty about the role of fish oil in cardiovascular disease, with reviews reaching different conclusions about its potential impact. Multiple evaluations suggest fish oil has little or no reduction on cardiovascular mortality, although there may be a small reduction in the incidence of actual cardiac events and strokes with its use.^[31][32][33] In 2007, the American Heart Association recommended the consumption of 1 gram of fish oil daily,^[34] preferably by eating fish, for patients with coronary artery disease, but cautioned pregnant and nursing women to avoid eating fish with high potential for mercury contaminants including mackerel, shark, and swordfish.^[35] (Optimal dosage was related to body weight.)

The US National Institutes of Health lists three conditions for which fish oil and other omega-3 sources are most highly recommended: hypertriglyceridemia (high triglyceride level), preventing secondary cardiovascular disease, and hypertension (high blood pressure). It then lists 27 other conditions for which there is less evidence. It also lists possible safety concerns: "Intake of 3 grams per day or greater of omega-3 fatty acids may increase the risk of bleeding, although there is little evidence of significant bleeding risk at lower doses. Very large intakes of fish oil or omega-3 fatty acids may increase the risk of hemorrhagic (bleeding) stroke."^[23]

There were studies to determine if fish oil had an effect on certain abnormal heart rhythms,^[36][37] although a 2012 meta-analysis found no significant effect.^[38]

A 2008 meta-study found fish oil supplementation did not demonstrate any preventative benefit to cardiac patients with ventricular arrhythmias.^[39] A 2012 meta-analysis covering 20 studies and 68,680 patients, found that omega-3 fatty acid supplementation did not reduce the chance of death, cardiac death, heart attack, or stroke.^[40] A 2018 meta-analysis of 77,000 participants found a 3% reduction in the relative risk for those who supplemented fish oil; however, this effect was deemed insignificant.^[41]

Hypertension

There have been some human trials that have concluded that consuming omega-3 fatty acids slightly reduces blood pressure (DHA could be more effective than EPA). Because omega-3 fatty acids can increase the risk of bleeding, a qualified healthcare provider should be consulted before supplementing with fish oil.^[42]

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