The association between dietary intakes of nitrate with nitrite from animal and plant food sources and the incidence of metabolic syndrome: a prospective study

In the current study the potential effect of dietary nitrate (NO3)/nitrite (NO2) on the incidence of metabolic syndrome (MetS) was investigated. Total of 1911 men and women (mean age of 37.5 ± 12.8 and 58.9% women), participated in the third (2006–2008) examinations of the Tehran Lipid and Glucose Study (TLGS), were included and followed up to 2018–2022. A semi-quantitative food frequency questionnaire was used at baseline to estimate dietary intakes of NO3 and NO2. Multivariable-adjusted Cox proportional hazard models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) of incidence of MetS across quartile categories of NO3 and NO2 dietary intakes. Mean (SD) daily intake of NO3 and NO2 were 436 (246) mg/d and 9.5 (4.7) mg/d, which were mostly derived from plant sources (95.2% and 56.1% respectively). The highest compared to the lowest quartile of total and plant-based dietary NO3 was accompanied with a significant decreased risk of MetS (HR = 0.73, 95% CI = 0.54–0.98, HR = 0.75, 95% CI = 0.56-1.00); however, no significant association was observed between animal-based NO3 intakes and incidence of MetS. Morover, no significant association between total, plant-based and animal-based dietary intakes of NO2 and the incidence of MetS was found. Higher total and plant-based NO3 intakes may reduce risk of MetS in adults.