Dietary Nitrate Reduces Blood Pressure And Improves Walking Economy And Cognitive Function In Older People

Abstract

Nitric oxide (NO), produced by the enzyme nitric oxide synthase (NOS), is a signalling molecule that regulates vascular tone, neurotransmission and mitochondrial function. NOS activity declines in older age contributing to increased morbidity and reduced exercise capacity. Increasing the intake of dietary inorganic nitrate (NO3-) might elevate NO bioavailability via an alternative NO3- -nitrite (NO2-) -NO reduction pathway and therefore compensate for NOS dysfunction. PURPOSE: To determine whether dietary supplementation with nitrate-rich (BR), compared to nitrate-depleted (PL), beetroot juice in healthy older adults will reduce blood pressure (BP), lower pulmonary O2 uptake (VO2) during walking and improve cognitive function. METHODS: 30 participants (age 73±3 yr, BMI 25±3 kg/m2) underwent 10-day supplementation periods with BR (~0.6 g NO3-/d) and PL (negligible NO3-) separated by a 10-day wash-out in a double-blind randomised cross-over design. The speed and accuracy of components of cognitive function were assessed via a computer-based Rapid Visual Information Processing (RVIP) test. Pulmonary VO2 was measured during three 6-min bouts of walking at 80% of gas exchange threshold. RESULTS: Plasma [NO3-] and [NO2-] were greater after BR (361 ± 55 μM and 969 ± 687 nM) than PL (34 ± 26 μM and 162 ± 96 nM) (both P<0.05). Systolic BP was lower after BR (124 ± 14 mmHg) than PL (129 ± 15 mmHg; P<0.05) but diastolic BP was not different between BR (69 ± 7 mmHg) and PL (70 ± 8 mmHg; P>0.05). Steady state VO2 during treadmill walking was lower after BR (861 ± 195 mL/min) than PL (892 ± 196 mL/min; P<0.05). The number of correct responses (BR: 20 ± 5, PL: 19 ± 6; P>0.05) and reaction time (BR: 726 ± 200, PL: 715 ± 146 ms; P>0.05) during the RVIP test were not different, but the number of errors made was lower in BR (6 ± 8) than PL (10 ± 11; P<0.05). CONCLUSIONS: The 4% reduction in systolic BP following BR may reduce the incidence of adverse cardiovascular events in older age. The lower O2 cost of walking and the lower number of errors made in the RVIP task in BR compared to PL suggests positive effects on cellular metabolism and cognitive function following NO3- supplementation. Collectively, these findings may have important implications for enhancing quality of life in older age.