Ageing modifies acute resting blood pressure responses to incremental consumption of dietary nitrate: a randomised, cross-over clinical trial

Beetroot is a rich source of nitrate (NO_3-) that has been shown to reduce blood pressure (BP). Yet, no studies have examined the vascular benefits of beetroot in whole-food form and whether the effects are modified by age. This study was a four-arm, randomised, open-label, crossover design in 24 healthy adults (young n=12, age 27±4 years, old n=12, age 64±5 years). Participants consumed whole cooked beetroot at portions of (NO_3- content in brackets) 100 (272mg), 200 (544mg) and 300g (816mg), and a 200ml solution containing 1000mg of potassium nitrate (KNO₃) on 4 separate occasions over a 4-week period (≥7-day washout period). BP, plasma NO_3- and nitrite (NO_2-) concentrations, and post-occlusion reactive hyperaemia (PORH) via laser Doppler, were measured pre and up to 5 hours post-intervention. Data were analysed by repeated measures analysis of variance. Plasma NO_2- concentrations were higher in the young vs. old at baseline and post-intervention (P<0.05). All NO_3- interventions decreased systolic and diastolic BP in young participants (P<0.05) whereas only KNO₃ (at 240-300 min post-intake) significantly decreased systolic (-4.8 mmHg, -3.5%, P=0.024) and diastolic (-5.4 mmHg, -6.5%, P=0.007) BP in older participants. In conclusion, incremental doses of dietary NO_3- reduced systolic and diastolic BP in healthy young adults whereas in the older group a significant decrease was only observed with the highest dose. The lower plasma NO_2- concentrations in older participants suggests there may be mechanistic differences in the production of NO from dietary NO_3- in young and older populations.