The association between dietary intakes of nitrate and nitrite and odds of metabolic syndrome and its component in adults

Metabolic syndrome (MetS), a cluster of conditions including central obesity, elevated blood pressure, high fasting blood glucose, high triglycerides, and low high-density lipoprotein cholesterol (HDL-C) cholesterol, has increased in prevalence worldwide. The evidence on the association between intakes of nitrate (NO3−) and nitrite (NO2−) and MetS is scarce and inconsistent. This study examined the association between dietary intakes of NO3− and NO2− with MetS in Iranian adults. This cross-sectional study was conducted on the baseline phase of the Tehran University of Medical Sciences Employee’s Cohort study (TEC). A total of 4027 adults aged 20 years or over were included (mean age: 40.72 ± 8.68 years). Dietary intakes of NO3− and NO2− were estimated using a validated dish-based food frequency questionnaire (FFQ) with 144 items. MetS was defined according to the diagnostic criteria proposed by the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP). Data were analyzed using independent t-tests, chi-square tests, ANOVA, ANCOVA, and logistic regression models adjusted for potential confounders. A P-value < 0.05 was considered statistically significant. While there was no significant association between the highest intake of NO3– and MetS, participants in the third quintile of NO3– were less likely to have MetS. However, no significant association between NO2 – and MetS intake was observed. Adults with the highest intake of NO3− were 26%, 30%, and 25% lower odds of having hypertension (HTN), low HDL-C, and abdominal obesity compared to the lowest intake. Furthermore, participants with the highest intake of NO2− compared to the lowest intake were 56%, 21%, and 22% lower odds of having hypertension, abdominal obesity, and low HDL-C, respectively (P < 0.05). While a negative association between NO2– and NO3− intake from plant sources and HTN and low HDL-C, a positive association between NO2– and NO3− intake from animal sources and HTN and hyperglycemia. Our findings showed that higher intakes of nitrate and nitrite were associated with lower odds of several MetS components. Further prospective studies are needed to provide evidence to compare with our findings.