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Department of Pharmacological Sciences University of Milan Via Balzaretti 9 20133 Milan Italy E-mail: francesco.visioli{at}unimi.it
Dear Sir:
Oomen et al (1) reported on the lack of association between -linolenic acid (ALA, 18:3n-3) consumption and the incidence of coronary artery disease in a 10-y follow-up. We believe that 2 major limitations of this study might have affected its outcome and led to the wrong conclusions. First, this study did not control for plasma concentrations of -linolenic acid; it is thus difficult to establish a causal relation between actual plasma concentrations of -linolenic acid—and of its elongation products eicosapentaenoic acid (22:5n-3) and docosahexaenoic acid (22:6n-3)—and the incidence of coronary artery disease. In contrast, the only clinical study of -linolenic acid carried out thus far, the Lyon Diet Heart Study (2, 3), proved that supplementation with adequate and controlled amounts of ALA increases plasma concentrations of this fatty acid, which was the only fatty acid significantly associated with an improved prognosis (3). Second, the amounts of ALA consumed by the subjects in the Zutphen Elderly Study were estimated only on the basis of food tables and dietary recollection data. Although food-composition tables may provide acceptable estimates of the intakes of major fatty acids, it is questionable whether such tables provide acceptable estimates of the intakes of minor fatty acids such as ALA that are present in amounts rarely exceeding 1 g/kg. Conversely, in the Lyon Diet Heart Study, patients were provided with known amounts of margarine enriched in ALA so that the daily intake of this fatty acid in the experimental and control groups was reliably determined to be 2 and 0.69 g, respectively. These differential intakes resulted in a 2-fold increase in the plasma concentrations of ALA in the experimental group (2). In conclusion, despite growing evidence that suggests health effects of ALA (4), we believe that because of the absence of reliable quantitative data, no definitive conclusions should be drawn regarding the health effects of ALA in terms of either plasma concentrations or daily intake.
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