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

BACKGROUND: The relationship between stable isotope ratios and dietary protein sources has been reported. However, few studies have examined the effect of stable isotope ratios on metabolic risk in humans. We investigated whether the stable isotope ratios of carbon and nitrogen in human hair are associated with blood pressure and hypertension. METHODS: We conducted a cross-sectional study of 392 subjects (228 men and 164 women). Hair samples of the subjects were used for the measurement of stable isotope ratios of carbon (δ(13)C) and nitrogen (δ(15)N). RESULTS: The δ(13)C and δ(15)N values showed positive correlations with diastolic blood pressure in the subjects without antihypertensive medication. In the subjects without antihypertensive medication, the multivariable-adjusted odds ratio (95% confidence interval) for hypertension was 1.55 (1.04–2.30) per 1‰ increase in δ(15)N and 1.22 (0.86–1.73) per 1‰ increase in δ(13)C, respectively. However, in the subjects with antihypertensive medication, neither δ(13)C nor δ(15)N values showed a significant association with hypertension. CONCLUSIONS: The stable isotopic ratio of nitrogen in scalp hair is independently associated with hypertension in subjects without antihypertensive medication. The hair δ(15)N value might be used as a surrogate marker to screen a high-risk population for hypertension.