Fish Oil (Omega-3)
Brief description
Fish oil is a popular supplement and a rich source of two long chained omega-3 polyunsaturated fatty acids – eicopentaenoic acid (EPA) and docosahexaenoic acid (DHA).
High doses of fish oil can be found in the following foods:
Mackerel (4,580 mg of EPA and DHA (combined) in 3.5 oz (100 g))
Salmon (2,150 mg of EPA and DHA (combined) in 3.5 oz (100 g))
Cod liver oil (2,438 mg of EPA and DHA (combined) per tablespoon)
For those who don’t eat fish, Alpha-Linolenic acid (ALA) is the plant based omega-3:
Flaxseed (2,350 mg of ALA per tablespoon (10.3 g) of whole seeds, or 7,260 mg per tablespoon (13.6 g) of oil)
Chia Seed (5,050 mg of ALA per oz (28g))
Walnuts (2,570 mg of ALA per oz (28 g), or about 14 walnut halves)
Popular health beliefs are that fish oil can reduce the risk of heart disease, cancer, and improve cholesterol.
Evidence base
Heart disease: Previous research has suggested no benefit of omega-3 supplementation on risk of cardiovascular disease (Heart attack, stroke, cardiac death)(1-3).
However, conflicting evidence remains - a 2019 meta-analysis of 13 trials (127,477 participants, 59% male, BMI ~28kg/m2, age ~64.3 yrs), with varying dosage of fish oil supplementation (376-4000mg/day) found a statistically significant reduction in risk of Heart attack (MI), total cardiovascular disease (CVD), cardiovascular death and that higher doses of omega-3 reduced risk of total CVD and major vascular events(4). Most trials tested doses of <1000mg/day.
Another, more recent (2020) systematic review (86 trials, 162,796 participants) found little to no effect of omega-3 on the same above outcomes, but a slight reduction in coronary heart disease events (number needed to benefit 167, RR 0.91, 95% CI 0.85 to 0.97; 134,116 participants)(5).
Cholesterol: A 2024 meta-analysis of 16 trials found that supplementation significantly reduced triglyceride levels (WMD: - 25.50 mg/dl, 95% CI: - 42.44, - 8.57, P = 0.000) compared to corn oil. It also had a significant positive effect on HDL (WMD: 2.54 mg/dl, 95% CI: 0.55, 4.52), but not LDL or Total cholesterol(6). Reduction of triglyceride levels were also consistent in those that were type 2 diabetic(7, 8).
Cancer: Poor evidence for supplementation of omega-3 and reduction in cancer types – findings from 57 meta-analyses(9).
Recommended serving & duration.
- Many trials examining outcomes of cardiovascular disease or cholesterol suggested a dose of at least 1g per day.
Safety & tolerability
Common side effects include:
Stomach discomfort.
Fishy breath, burps (dyspepsia)
Reflux, nausea and or diarrhoea.
Atrial Fibrillation.
To minimise this, consider supplementing with meals, or increase dietary intake of natural omega 3.
Systematic reviews and meta-analyses of clinical trials have highlighted a dose-dependent increased risk of atrial fibrillation in patients with cardiovascular diseases or risk factors taking omega-3-acid ethyl ester medicines, compared with placebo; the observed risk was found to be highest at a dose of 4 g daily [NICE Guideline/MHRA]
If there is any doubt about whether omega-3 is safe for you to take, please consult with your healthcare provider.
References
Rizos EC, Ntzani EE, Bika E, Kostapanos MS, Elisaf MS. Association between omega-3 fatty acid supplementation and risk of major cardiovascular disease events: a systematic review and meta-analysis. Jama. 2012;308(10):1024-33.
Kwak SM, Myung SK, Lee YJ, Seo HG. Efficacy of omega-3 fatty acid supplements (eicosapentaenoic acid and docosahexaenoic acid) in the secondary prevention of cardiovascular disease: a meta-analysis of randomized, double-blind, placebo-controlled trials. Arch Intern Med. 2012;172(9):686-94.
Aung T, Halsey J, Kromhout D, Gerstein HC, Marchioli R, Tavazzi L, et al. Associations of Omega-3 Fatty Acid Supplement Use With Cardiovascular Disease Risks: Meta-analysis of 10 Trials Involving 77 917 Individuals. JAMA Cardiol. 2018;3(3):225-34.
Hu Y, Hu FB, Manson JE. Marine Omega-3 Supplementation and Cardiovascular Disease: An Updated Meta-Analysis of 13 Randomized Controlled Trials Involving 127 477 Participants. J Am Heart Assoc. 2019;8(19):e013543.
Brainard JS, Jimoh OF, Deane KHO, Biswas P, Donaldson D, Maas K, et al. Omega-3, Omega-6, and Polyunsaturated Fat for Cognition: Systematic Review and Meta-analysis of Randomized Trials. J Am Med Dir Assoc. 2020;21(10):1439-50.e21.
Safaei P, Bayat G, Mohajer A. Comparison of fish oil supplements and corn oil effects on serum lipid profile: a systematic review and meta-analysis of randomized controlled trials. Syst Rev. 2024;13(1):54.
Zhang M, Yang F, Feng Q, Ou Y, Zhang J, Wan H, et al. Comparison of the efficacy of fish oil and probiotic supplementation on glucose and lipid metabolism in patients with type 2 diabetes: a systematic review and network meta-analysis. Diabetol Metab Syndr. 2024;16(1):25.
Xiao Y, Zhang Q, Liao X, Elbelt U, Weylandt KH. The effects of omega-3 fatty acids in type 2 diabetes: A systematic review and meta-analysis. Prostaglandins Leukot Essent Fatty Acids. 2022;182:102456.
Lee KH, Seong HJ, Kim G, Jeong GH, Kim JY, Park H, et al. Consumption of Fish and ω-3 Fatty Acids and Cancer Risk: An Umbrella Review of Meta-Analyses of Observational Studies. Adv Nutr. 2020;11(5):1134-49.
