Alpha-Linolenic Acid

Abstract

Although the fish-derived, long-chain omega-3 fatty acids (n-3 FA) may be considered “gifts from the sea” for cardiovascular health, the role of the land (or plant) -based n-3 FA α-linolenic acid (ALA) has been less clear. ALA is the 18-carbon, 3-double bond (C18:3n-3) precursor to eicosapentaenoic acid (EPA; C20:5n-3) and docosahexaenoic acid (DHA; C22:6n-3), the latter 2 being the predominant n-3 FA in fish oils. ALA is found in certain plant oils, most notably flaxseed oil (where it constitutes ≈50% of total FA) and in canola oil (≈9%), unhydrogenated soybean (salad dressing) oil (≈7%), hydrogenated soybean oil (≈3%), and olive oil (≈1%). According to National Health and Nutrition Examination Survey (NHANES) III data, consumption in the United States currently averages ≈1.3 g/d. See p 2921 Could ALA substitute for EPA+DHA to reduce risk for coronary heart disease (CHD) mortality? This question presumes that ALA can be bioconverted to the longer-chain n-3 FA, but the extent to which this occurs is unclear. Depending on the method used, estimates for the conversion to EPA run from 0.2% to 7% to 10%.1 Further conversion to DHA is reported to be ≈0.05% in men and 10% in women. Ultimately, bioequivalence will need to be demonstrated in randomized controlled trials (RCTs), not in metabolic studies. The latest epidemiological contribution to the ALA story is reported in this issue of Circulation . Djousse et al2 continue to mine the fertile database of the National Heart, Lung, and Blood Institute’s Family Heart Study (FHS) to explore the relationships between nutrition and CHD. In this study, they examined the association between coronary artery calcification and the estimated intake of linolenic acid (LNA) obtained in 2004 subjects ≈7 years earlier. (LNA includes two 18-carbon, 3-double bond FA: α- and γ-linolenic acid. The latter is an n-6 FA …