Red blood cell delta15N: a novel biomarker of dietary eicosapentaenoic acid and docosahexaenoic acid intake.

Background: The long-chain omega-3 (n-3) fatty acids derived from fish, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are associated with a reduced risk of cardiovascular disease and other chronic diseases. Study of the associations between EPA and DHA intake and disease requires a valid biomarker of dietary intake; however, the direct measurement of tissue fatty acid concentrations is expensive and time consuming.

Objective: Because the nitrogen stable isotope ratio ((15)N/(14)N, expressed as delta(15)N) is elevated in fish, we investigated whether delta(15)N is a valid alternative biomarker of EPA and DHA intake.

Design: We examined the relation between red blood cell (RBC) delta(15)N and RBC EPA and DHA in a community-based sample of 496 Yup'ik Eskimos with widely varying intake of n-3 fatty acids. We also assessed the correlation between delta(15)N and dietary EPA and DHA intake based on 24-h dietary recalls and 3-d food records completed by a subset of 221 participants.

Results: RBC delta(15)N was strongly correlated with RBC EPA and DHA (r = 0.83 and 0.75, respectively). These correlations differed only modestly by sex and age class. RBC delta(15)N also correlated with dietary EPA and DHA intake (r = 0.47 and 0.46, respectively) and did not differ by sex and age.

Conclusions: The results strongly support the validity of RBC delta(15)N as a biomarker of EPA and DHA intake. Because the analysis of RBC delta(15)N is rapid and inexpensive, this method could facilitate wide-scale assessment of EPA and DHA intake in clinical and epidemiologic studies.