High- and low-nitrate vegetable intake produce similar effects on redox, inflammatory, and cardiometabolic markers in older adults: a randomized crossover trial

PURPOSE: To compare effects of high-nitrate (HN) and low-nitrate (LN) vegetable intake on redox, inflammatory, and cardiometabolic biomarkers in community-dwelling older adults. METHODS: In this randomized, crossover trial, 39 older adults ≥60 years consumed 250 g/day of either HN or LN vegetables for 7 days, separated by a 7-day washout period. Assessments before and after each intervention included plasma and urinary NOx (nitrate and nitrite), blood pressure, lipid profile, triglyceride-glucose (TyG) index, antioxidant enzyme activities (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx], glutathione S-transferase [GST]), serum total antioxidant capacity (sTAC), oxidative damage markers (malondialdehyde [MDA], protein carbonyls), cytokines (IL-6, IL-10; reduced subsamples, n = 18 and n = 35, respectively), and dietary/physical activity recalls. Treatment effects (HN vs. LN) were assessed using covariate-adjusted linear mixed-effects models (p < 0.05); effect size was calculated as Cohen's d (|d|). RESULTS: The HN intervention provided a measured mean nitrate intake of 431.5 ± 163.6 mg/day and substantially increased plasma and urinary NOx concentrations compared to LN (p < 0.001). However, this did not translate into significant differences in any redox, inflammatory, or cardiometabolic markers (all p > 0.05). Effect sizes for between-intervention comparisons were consistently small (|d| ≤ 0.40), with the largest effects observed for GST (|d| = 0.40), TyG index (|d| = 0.32), and systolic blood pressure (|d| = 0.28). CONCLUSIONS: No incremental contribution of nitrate-rich vegetable matrices to redox, inflammatory, or cardiometabolic markers was detected. The clinical relevance of nitrate-rich vegetables may be more apparent in populations with compromised vascular or metabolic function. CLINICAL TRIAL REGISTRY NUMBER: RBR-102bc3f2, website: https://ensaiosclinicos.gov.br/rg/RBR-102bc3f2. Date of registration: 26th September, 2022.