Abstract
Nitrate-rich food can increase nitric oxide production and improve vascular and brain functions. This study examines the feasibility of a randomised controlled trial (RCT) testing the effects of prolonged consumption of different doses of dietary nitrate (NO3-) in the form of beetroot juice (BJ) in overweight and obese older participants. A single-blind, four-arm parallel pilot RCT was conducted in 62 overweight and obese (30.4 +/- 4 kg/m(2)) older participants (mean +/- standard deviation (SD), 66 +/- 4 years). Participants were randomized to: (1) high-NO3- (HN: 2 x 70 mL BJ/day) (2) medium-NO3- (MN: 70 mL BJ/day), (3) low-NO3- (LN: 70 mL BJ on alternate days) or (4) Placebo (PL: 70 mL of NO3--depleted BJ on alternate days), for 13 weeks. Compliance was checked by a daily log of consumed BJ, NO3- intake, and by measuring NO3- and NO2- concentrations in plasma, saliva, and urine samples. Fifty participants completed the study. Self-reported compliance to the interventions was >90%. There were significant positive linear relationships between NO3- dose and the increase in plasma and urinary NO3- concentration (R-2 = 0.71, p < 0.001 and R-2 = 0.46 p < 0.001, respectively), but relationships between NO3- dose and changes in salivary NO3- and NO2- were non-linear (R-2 = 0.35, p = 0.002 and R-2 = 0.23, p = 0.007, respectively). The results confirm the feasibility of prolonged BJ supplementation in older overweight and obese adults.