Vitamin C intake modify the impact of dietary nitrite on the incidence of type 2 diabetes: A 6-year follow-up in Tehran Lipid and Glucose Study

Abstract

Background: There is no epidemiological study on the association between dietary nitrate (NO₃) and nitrite (NO₂) and intakes and the risk of type 2 diabetes (T2D).

Objective: The aim of this study was therefore to examine the potential effect of dietary NO₃ and NO₂ on the occurrence of T2D.

Design: This longitudinal study was conducted within the framework of the Tehran Lipid and Glucose Study (TLGS) on 2139 T2D-free adults, aged 20-70 years, followed for a median of 5.8 y. Dietary intakes of NO₃ and NO₂ were estimated using a 168-food items validate semi-quantitative food frequency questionnaire, at baseline. Multivariate Hazard Ratios (HR) and 95% confidence intervals (CI), adjusted for diabetes risk score (DRS), and dietary intakes of fat, fiber and vitamin C, were calculated for residual energy-adjusted NO₃ and NO₂ intakes. Since significant interaction (P = 0.024) was found between NO₂ and vitamin C intakes in the multivariable model, stratified analyses were done for < and ≥ median vitamin C intakes.

Results: Median (inter quartile range; IQR) daily intake of NO₃ and NO₂ were 410 mg/d (343-499) and 8.77 mg/d (7.53-10.2). An increased risk of T2D was observed among participants who had higher intake of total and animal-based NO₂ in participants who had low vitamin C intake (HR = 2.43, 95% CI = 1.45-4.05, HR = 1.88, 95% CI = 1.12-3.15, respectively). We found no significant association between NO₃ in overall, and plant- and animal sources as well, with the risk of T2D. Plant-derived NO₂ was also unrelated to incidence of T2D.

Conclusion: Our findings indicated that higher intakes of total and animal-based NO₂ may be an independent dietary risk factor for development of T2D in subjects with lower vitamin C intakes.

Keywords: Nitrate; Nitrite; Type 2 diabetes; Vitamin C.