Dispelling the JAMA study's findings
Kimberly K. Reed, O.D., F.A.A.O
Recently, The Journal of the American Medical Association (JAMA) published a study revealing omega-3 fatty acid supplementation isn't associated with a decreased risk of all-cause mortality, cardiac death, sudden death, myocardial infarction and stroke, as has been widely believed.1 This has caused the public to question the prior widespread recommendation by medical professionals to take omega-3 fatty acid supplementation for a broad variety of systemic and ocular conditions or alter one's diet to include more omega-3 fatty acids.
Here, I discuss this study's flaws.
It's a meta-analysis study
The study's authors reviewed 20 randomized clinical trials that evaluated the effect of omega-3 on allcause mortality, cardiac death, sudden death, myocardial infarction and stroke to find similar trends or “treatment effects.” The upside to this method is that while an individual study might include data from a few hundred subjects, a meta-analysis study is comprised of subjects from many studies and potentially includes tens of thousands of subjects.
In the JAMA study, almost 70,000 subjects' data were included. Of course, typically we believe that the more subjects in a study, the more compelling its data. However, meta-analysis studies deserve a lot of critical review and analysis. This is because the study methodology is usually not identical across all the studies compiled, which can lead to erroneous conclusions.
Many types of omega-3s
Omega-3 fatty acids are a pretty large group of substances. Plant-based sources of shorter-chain omega-3s include walnuts and flax seeds, while marine-based sources of longer-chain omega-3s include algae and cold-water fatty fish. Conversion of the shorter-chain to the health-promoting longer-chain fatty acids varies from patient to patient and probably also varies from day-to-day based on a number of factors, such as the other foods eaten at or near the same time as the omega-3 food source.2,3
The nearly 70,000 subjects in this meta-analysis study took varying doses of omega-3s, mostly ranging between 1.0g and 1.5g per day of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). This is a fairly low dose compared with the 4.0g per day for “therapeutic” pharmaceutical grade omega-3 capsules that hightriglyceride patients take.
Omega-3 supplements are highly variable in content. A 1g capsule, for example, might contain high levels of alpha-linolenic acid, or ALA. This is the shorter-chain form of omega-3 found in plant sources that must be converted in several different processes into the longer forms of DHA and EPA to provide health benefits.
Other supplements might contain little or no ALA and much higher quantities of DHA and EPA. And while some supplements include specific concentration levels, others do not. All these variations directly affect dosage and concentration, and therefore the therapeutic levels in a patient's bloodstream. For example, “1000mg fish body oil” is a completely different supplement than “1000mg all natural omega-3.” And, although EPA and DHA are considered the “functional” omega-3s, we are just discovering which one (or both) may play a role in ocular and systemic health.
In addition, our knowledge continues to develop about the structure and function of individual omega-3 fatty acid sub-types, with a lot of interest focused on the molecular form of omega-3 supplements.
Specifically, supplements are available either in the form of ethyl esters (EE), or as re-esterified triglycerides (TG) (not to be confused with serum triglycerides). While still somewhat controversial, the majority of studies suggest that the TG form of omega-3s are better absorbed, and hence more bioavailable, than the EE form — but this is still fairly hotly debated among many leading experts.4,5
The supplements taken by the subjects across the 20 studies in the JAMA report were taken in various formulations, from various sources, containing various ratios of EPA and DHA. When you throw into this already confounding mix of variables the fact that the subjects were already diagnosed with cardiovascular disease and ate different foods while being treated, you can begin to see the difficulty of accepting the study's conclusion.
Literally hundreds of studies to date support the use of omega-3s for cardiovascular health support.6-10 The mechanisms by which omega-3s exert this apparent cardioprotective effect are probably multifactorial, perhaps including lowering triglyceride levels; modest decreases in blood pressure; decreasing inflammatory cytokines associated with cardiovascular disease risk; decreasing the viscosity of the blood and inhibiting platelet aggregation; among several other means. Also, an abundance of long-term studies of food intake in multiple populations reveal that high dietary intake of long-chain omega-3 fatty acids (specifically EPA and DHA) is associated with better health outcomes than lower dietary intake of these nutrients.11 Further, scores of other studies exist revealing the benefit of omega-3s on mood and affect disorders, autoimmune disease, cancer prevention, and, of course, ocular health promotion.12-15 Therefore, there is no reason for patients to cease their doctor-recommended omega-3 fatty acid supplementation or dietary changes. OM
References are available in the online version of this article at optometricman agement.com.
Omega-3s are involved in far more ocular functions than the ocular surface. In my next column, I review the roles these essential nutrients may play in ocular wellness, including reading speed, glaucoma, age-related macular degeneration and others.
|DR. REED IS AN ASSOCIATE PROFESSOR AT THE NOVA SOUTHEASTERN UNIVERSITY COLLEGE OF OPTOMETRY IN FORT LAUDERDALE, FLA., A MEMBER OF THE OCULAR NUTRITION SOCIETY AND AUTHOR OF NUMEROUS ARTICLES ON OCULAR NUTRITION, DISEASE AND PHARMACOLOGY, SHE IS ALSO A FREQUENT CONTINUING EDUCATION LECTURER. TO COMMENT ON THIS COLUMN, E-MAIL DR. REED AT KIM REED@NOVA.EDU.|
Optometric Management, Volume: 47 , Issue: October 2012, page(s): 56 71