The association between carbon and nitrogen stable isotope ratios of human hair and metabolic syndrome

•The first study to evaluate the potential clinical application of the stable isotope ratio in relation to metabolic syndrome•The nitrogen stable isotope ratio is associated with metabolic syndrome.•The nitrogen stable isotope ratio as a surrogate marker to assess metabolic syndrome

BackgroundIt has been reported that stable isotope ratios can be used as biomarkers for animal protein intake. Meat consumption and high protein intake could be risk factors for metabolic disorders. We investigated whether the stable isotope ratios of carbon and nitrogen are associated with metabolic syndrome.MethodsWe conducted a cross-sectional study of 399 subjects (233 men and 166 women). Hair samples from 399 subjects were measured for stable isotope ratios of carbon (δ13C) and nitrogen (δ15N).ResultsThe δ15N values progressively increased with the number of components of the metabolic syndrome present in study subjects (P for trend 0.047). In multivariable models, δ15N values were positively associated with the presence of metabolic syndrome (odds ratio, 1.53; 95% confidence interval, 1.09–2.14), whereas δ13C values were not (odds ratio, 0.97; 95% confidence interval, 0.72–1.30). The odds ratio (95% confidence interval) for metabolic syndrome comparing the highest to the lowest quartiles of δ15N values was 2.64 (1.17–5.92).ConclusionsThe nitrogen, but not carbon, stable isotopic ratio of hair is independently associated with the presence of metabolic syndrome. The hair δ15N value might be a surrogate marker for clustering of risk factors in metabolic syndrome.