Pharmacokinetic profile of incremental oral doses of dietary nitrate in young and older adults: a crossover randomized clinical trial

Background

Dietary nitrate consumption can increase concentrations of nitrate and nitrite in blood, saliva and urine. Whether the change in concentrations is influenced by age is currently unknown.

Objective

Measure changes in nitrate and nitrite concentrations in plasma, urine, saliva and exhaled nitric oxide (NO) concentrations following single incremental doses of dietary nitrate in young and older healthy adults.

Methods

12 young (18–35 years) and 12 older (60–75 years) healthy, non-smoking participants consumed single doses of 100g, 200g, 300g whole beetroot and 1000 mg potassium nitrate (positive control) at least 7 days apart in a crossover, randomized clinical trial. Plasma nitrate and nitrite concentrations, and exhaled NO levels were measured over a 5-hour period. Salivary nitrate and nitrite concentrations were measured over a 12-hour period and urinary nitrate over a 24-hour period. Time, intervention, age, and interaction effects were measured with repeated measures ANOVAs.

Results

Dose-dependent increases were seen in plasma, salivary and urinary nitrate following beetroot ingestion (all P ≤ 0.002) but there were no differences between age groups at baseline (all P ≥ 0.56) or post-intervention (all P ≥ 0.12). Plasma nitrite concentrations were higher in young than older participants at baseline (P = 0.04) and following consumption of 200g (P = 0.04; +25.7nmol/L; 95%CI: 0.97, 50.3) and 300g of beetroot (P = 0.02; +50.3 nmol/L; 95% CI: 8.57, 92.1). Baseline fractional exhaled NO (FeNO) levels were higher in the younger group (P = 0.03; +8.60ppb; 95%CI: 0.80, 16.3), and rose significantly over the 5-hour period, peaking after KNO3 5 h post (39.4 ± 4.5 ppb; P < 0.001); however, changes in FeNO were not influenced by age (P = 0.276).

Conclusions

Beetroot is a source of bioavailable dietary nitrate in both young and older adults and can effectively raise nitrite and nitrate concentrations. Lower plasma nitrite and FeNO concentrations were found in older subjects confirming the impact of ageing on NO bioavailability across different systems.