Relation between stable isotope ratios in human red blood cells and hair: implications for using the nitrogen isotope ratio of hair as a biomarker of eicosapentaenoic acid and docosahexaenoic acid.
BACKGROUND
The nitrogen isotope ratio (expressed as delta(15)N) of red blood cells (RBCs) is highly correlated with the RBC long-chain omega-3 (n-3) fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in Yup'ik Eskimos. Because delta(15)N can also be measured in hair samples, it could provide a noninvasive, retrospective biomarker for EPA and DHA intakes.


OBJECTIVE
We investigated the agreement between delta(15)N in hair and RBCs and then evaluated the relations between hair delta(15)N and RBC EPA and DHA. We also assessed the agreement in carbon isotope ratios (delta(13)C) between hair and RBCs, because delta(13)C has been proposed as a dietary biomarker in other populations.


METHODS
We assessed relations between hair and RBC delta(15)N and delta(13)C in a community-based sample of 144 Yup'ik Eskimos and examined the correlations between delta(15)N and RBC EPA and DHA in a subset of these participants (n = 44).


RESULTS
We showed a 1:1 relation with good agreement between hair and RBC delta(15)N (r = 0.91) and delta(13)C (r = 0.87). Hair isotope ratios were greater than RBC ratios by 1.5 per thousand for delta(15)N and by 2.3 per thousand for delta(13)C. There were strong correlations between hair delta(15)N and RBC EPA and DHA (r = 0.83 and 0.84, respectively).


CONCLUSIONS
These results support the use of hair delta(15)N values as a biomarker of EPA and DHA intakes. Because hair collection is noninvasive and the samples require no special processing, studies of EPA and DHA intakes in large populations could use biomarkers rather than self-reports to assess these fatty acids.
Center for Alaska Native Health Research, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA.
Sarah H
SH
Nash
Alan R
AR
Kristal
Bert B
BB
Boyer
Irena B
IB
King
Jordan S
JS
Metzgar
Diane M
DM
O'Brien
D000293:Adolescent; D000328:Adult; D000368:Aged; D015415:Biomarkers; D004281:Docosahexaenoic Acids / Q000008:administration & dosage*; D015118:Eicosapentaenoic Acid / Q000008:administration & dosage*; D004912:Erythrocytes / Q000378:metabolism*; D005260:Female; D006197:Hair / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009587:Nitrogen Isotopes / Q000378:metabolism*
D015415:Biomarkers; D009587:Nitrogen Isotopes; D004281:Docosahexaenoic Acids; D015118:Eicosapentaenoic Acid