The association between dietary intakes of nitrate with nitrite from animal and plant food sources and the incidence of pre-diabetes and type 2 diabetes: a prospective study

We investigated the potential effect of dietary nitrate (NO3)/nitrite (NO2) on the incidence of pre-diabetes (Pre-DM) and type 2 diabetes (T2D). This longitudinal study was conducted on 2417 T2D- and Pre-DM free adults, aged 21-70 years (mean age of 39.6 ± 13.3 and 45.8% men) who participated in the third (2006-2008) examinations of the Tehran Lipid and Glucose Study (TLGS) and followed up to 2018-2022. The participants' habitual dietary intakes of NO3 and NO2 were estimated using a semi-quantitative food frequency questionnaire (FFQ) at baseline. Multivariable-adjusted Cox proportional hazard models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) of incidence of Pre-DM and T2D across quartile categories of NO3 and NO2 intakes. Mean (SD) daily intake of NO3 and NO2 were 489 (206) mg/d and 9.6 (3.8) mg/d; NO3 intakes mainly were derived from plant sources (95.7%). The highest compared to the lowest quartile of total and plant-based dietary NO3 intakes was accompanied by a significantly decreased risk of Pre-DM (HR = 0.65, 95% CI = 0.50-0.85, HR = 0.68, 95% CI = 0.52-0.88). A reduced risk of T2D was observed in medium intakes of NO3 (HR = 0.68, 95% CI = 0.47-0.97, HR = 0.70, 95% CI = 0.49-1.00, in the total and plant-based sources, respectively). The lowest compared to the highest quartile of dietary NO2 was accompanied by a reduced incidence of T2D (HR = 0.71, 95% CI = 0.51-0.98, HR = 0.61, 95% CI = 0.44-0.84 in the total and plant-based sources, respectively). Higher and medium intakes of NO3 are associated with a reduced incidence of Pre-DM and T2D, respectively.