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

Background: It 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.

Methods: We 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 (δ(13)C) and nitrogen (δ(15)N).

Results: The δ(15)N values progressively increased with the number of components of the metabolic syndrome present in study subjects (P for trend 0.047). In multivariable models, δ(15)N values were positively associated with the presence of metabolic syndrome (odds ratio, 1.53; 95% confidence interval, 1.09-2.14), whereas δ(13)C 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 δ(15)N values was 2.64 (1.17-5.92).

Conclusions: The nitrogen, but not carbon, stable isotopic ratio of hair is independently associated with the presence of metabolic syndrome. The hair δ(15)N value might be a surrogate marker for clustering of risk factors in metabolic syndrome.