Dietary nitrate does not have an effect on physical activity outcomes in healthy older adults : a randomized, cross-over trial

Dietary nitrate (〖NO〗_3^-) ingestion appears to enhance exercise capacity and performance in young individuals whereas inconclusive findings have been reported in older people. We conducted a double-blind, cross-over randomized clinical trial in older normal weight and overweight healthy participants testing whether beetroot juice (a rich source of 〖NO〗_3^-) for one week may increase nitric oxide bioavailability via the non-enzymatic pathway and enhance 1) exercise capacity during an incremental exercise test, 2) physical capability and 3) free-living physical activity. Twenty non-smoking healthy participants aged 60-75y and BMI 20.0-29.9kg/m2 were included. Pre and post supplementation resting, sub-maximal, maximal and recovery gas exchanges were measured. Physical capability was measured by hand-grip strength (HGS), time-up-and-go (TUG), repeated-chair-rising-test (RCRT), and 10m walking speed (WLS). Free-living physical activity was assessed by triaxal accelerometry. Changes in urinary and plasma 〖NO〗_3^- concentrations were measured by gas chromatography mass spectrometry. Nineteen participants (M/F=9/10) completed the study. Beetroot juice increased significantly both plasma and urinary 〖NO〗_3^- concentrations (p<0.001) compared to placebo. Beetroot juice did not influence resting, sub-maximal and maximal oxygen consumption during the incremental exercise test. In addition, measures of physical capability and physical activity levels measured in free-living conditions were not modified by beetroot juice ingestion. The positive effects of beetroot juice ingestion on exercise performance seen in young individuals were not replicated in healthy, older adults. Whether aging represents a modifier of the effects of dietary 〖NO〗_3^- on muscular performance is not known and mechanistic studies and larger trials are needed to test this hypothesis. Keywords: inorganic nitrate, nitric oxide, exercise, oxygen consumption, aging