Comparison between plasma and erythrocyte fatty acid content as biomarkers of fatty acid intake in US women.

BACKGROUND Erythrocyte fatty acids may be superior to plasma fatty acids for reflecting long-term fatty acid intake because of less sensitivity to recent intake and a slower turnover rate. OBJECTIVE The objective was to compare the fatty acid content of erythrocytes with that of plasma with respect to their abilities to reflect usual fatty acid intake. DESIGN Fatty acids in plasma and erythrocytes were measured by capillary gas-liquid chromatography in 306 US women aged 43-69 y. Fatty acid intake was assessed with a food-frequency questionnaire, which was validated for measuring intakes of various fatty acids. RESULTS Docosahexaenoic acid (DHA, 22:6n-3) in erythrocytes and plasma provided the strongest correlations with its intake, but erythrocyte DHA concentrations [Spearman's partial correlation coefficient (r(s))=0.56] were better than plasma DHA concentrations (r(s)=0.48) as a biomarker. Total trans fatty acids (r(s)=0.43) and total 18:1 trans isomers (r(s)=0.42) in erythrocytes were also more strongly correlated with intake than were those in plasma (r(s)=0.30 and r(s)=0.29, respectively). Moderate correlations were observed for linoleic acid (18:2n-6; erythrocytes, r(s)=0.24; plasma, r(s)=0.25), alpha-linolenic acid (18:3n-3; erythrocytes, r(s)=0.18; plasma, r(s)=0.23), and eicosapentaenoic acid (20:5 n-3; erythrocytes, r(s)=0.38; plasma, r(s)=0.21). For polyunsaturated and trans fatty acids, correlations between intakes and biomarkers improved moderately when average intakes over previous years were used. CONCLUSION Erythrocyte n-3 fatty acids of marine origin and trans fatty acid content are suitable biomarkers for long-term intake.