Critical Differences Between Dietary Supplement and Prescription Omega-3 Fatty Acids: A Narrative Review

Abstract

Introduction: Currently available omega-3 (OM-3) fatty acid products in the US are either nonprescription dietary supplements (e.g., fish oils) or prescription (Rx) medications. As such, we aimed to describe critical therapeutic differences among the OM-3 fatty acids, focusing on differences between fish oil supplements and Rx OM-3s.

Methods: A narrative review of known papers salient to this topic was conducted.

Results: Despite the multiple purported clinical benefits, the published evidence for OM-3 dietary supplements is generally insufficient, inconsistent, or negative. Rx OM-3 products are indicated as an adjunct to diet to reduce triglycerides (TG) in adults with severe hypertriglyceridemia (TG ≥ 500 mg/dl). Recently, the Rx eicosapentaenoic acid (EPA)-only OM-3, icosapent ethyl, demonstrated cardiovascular (CV) risk reduction among statin-treated patients at high risk of CV disease in a large CV outcomes trial (CVOT), and is now also indicated as an adjunct to maximally tolerated statin therapy to reduce the risk of myocardial infarction, stroke, coronary revascularization, and unstable angina requiring hospitalization in adult patients with elevated TG (≥ 150 mg/dL) and established CVD or diabetes mellitus and ≥ 2 additional risk factors for CVD. In contrast to the rigorous regulatory standards for safety, efficacy, and manufacturing of medications (whether Rx or over the counter), the Food and Drug Administration manages dietary supplements as food. Issues specific to OM-3 dietary supplements include variable content, labeling inconsistencies, and poor product quality/impurity. Given these issues, OM-3 dietary supplements should not be substituted for Rx OM-3 products. The efficacy of the EPA-only Rx OM-3 product in a large CVOT cannot be extrapolated to other OM-3 products.

Conclusion: Consumers and health care providers need to recognize critical differences between Rx and OM-3 dietary supplements to ensure appropriate use of each OM-3 product.

Keywords: Cardiovascular disease; Dietary supplements; Docosahexaenoic acid; Eicosapentaenoic acid; Fish oils; Hypertriglyceridemia; Icosapent ethyl; Omega-3-fatty acids.

Fig. 1

Variable and inconsistent omega-3 content of dietary supplements. a Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) comprise < 75% of the entire fat content of three different omega-3 dietary supplements available in the US. EPA, DHA, saturated fats, and other fats (consisting of mono- and polyunsaturated fatty acids) are presented as % of total fatty acids by weight [60]. b In a study evaluating the actual omega-3 content of widely available fish oil dietary supplements sold in New Zealand, only 3 of 32 products for which OM3 content was measured contained EPA and DHA at levels equal to or higher than that stated on their labels, and the majority contained < 67% of their stated label content [61]. The dotted line indicates claimed level of OM-3 content. Adapted with permission from Mason 2017 [60] and Albert 2015 [61]

Fig. 2

Oxidation product content in top-selling OM-3 dietary supplements. a In a study of omega-3 dietary supplements available in the US, all three evaluated had oxidation product levels that exceeded recommended levels. The one prescription product evaluated had much lower levels of oxidation products [60]. b In a study of 36 omega-3 fish oil dietary supplements sold in New Zealand, half of the products exceeded recommended oxidation levels [61]. Dotted lines indicate recommended international thresholds including those recommended by the US Council for Responsible Nutrition. Adapted with permission from Mason 2017 [60] and Albert 2015 [61]

Fig. 3

Differences in purity between fish oil supplements and Rx OM-3s [8, 19]. Composition of dietary supplements can vary greatly between products [60]