Serum carbon and nitrogen stable isotopes as potential biomarkers of dietary intake and their relation with incident type 2 diabetes: the EPIC-Norfolk study (original) (raw)

Background: Stable-isotope ratios of carbon ( 13 C/ 12 C, expressed as d 13 C) and nitrogen ( 15 N/ 14 N, or d 15 N) have been proposed as potential nutritional biomarkers to distinguish between meat, fish, and plant-based foods. Objective: The objective was to investigate dietary correlates of d 13 C and d 15 N and examine the association of these biomarkers with incident type 2 diabetes in a prospective study. Design: Serum d 13 C and d 15 N (&) were measured by using isotope ratio mass spectrometry in a case-cohort study (n = 476 diabetes cases; n = 718 subcohort) nested within the European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk populationbased cohort. We examined dietary (food-frequency questionnaire) correlates of d 13 C and d 15 N in the subcohort. HRs and 95% CIs were estimated by using Prentice-weighted Cox regression. Results: Mean (6SD) d 13 C and d 15 N were 222.8 6 0.4& and 10.2 6 0.4&, respectively, and d 13 C (r = 0.22) and d 15 N (r = 0.20) were positively correlated (P , 0.001) with fish protein intake. Animal protein was not correlated with d 13 C but was significantly correlated with d 15 N (dairy protein: r = 0.11; meat protein: r = 0.09; terrestrial animal protein: r = 0.12, P # 0.013). d 13 C was inversely associated with diabetes in adjusted analyses (HR per tertile: 0.74; 95% CI: 0.65, 0.83; P-trend , 0.001], whereas d 15 N was positively associated (HR: 1.23; 95% CI: 1.09, 1.38; P-trend = 0.001). Conclusions: The isotope ratios d 13 C and d 15 N may both serve as potential biomarkers of fish protein intake, whereas only d 15 N may reflect broader animal-source protein intake in a European population. The inverse association of d 13 C but a positive association of d 15 N with incident diabetes should be interpreted in the light of knowledge of dietary intake and may assist in identifying dietary components that are associated with health risks and benefits. Am J Clin Nutr