Dietary nitrate does not affect physical activity or outcomes in healthy older adults in a randomized, cross-over trial

Abstract

Although dietary nitrate (NO₃^-) ingestion appears to enhance exercise capacity and performance in young individuals, inconclusive findings have been reported in older people. Therefore, we conducted a double-blind, crossover randomized clinical trial using beetroot juice in older healthy participants, who were classified as normal weight and overweight. We tested whether consumption of beetroot juice (a rich source of NO₃^-) for 1 week would increase nitric oxide bioavailability via the nonenzymatic pathway and enhance (1) exercise capacity during an incremental exercise test, (2) physical capability, and (3) free-living physical activity. Twenty nonsmoking, healthy participants between 60 and 75 years of age and with a body mass index of 20.0 to 29.9 kg/m² were included. Presupplementation and postsupplementation resting, submaximal, maximal, and recovery gas exchanges were measured. Physical capability was measured by hand-grip strength, time-up-and-go, repeated chair rising test, and 10-m walking speed. Free-living physical activity was assessed by triaxal accelerometry. Changes in urinary and plasmaNO₃^-concentrations were measured by gas chromatography-mass spectrometry. Nineteen participants (male-to-female ratio, 9:10) completed the study.Beetroot juice increased significantly both plasma and urinary NO₃^-concentrations (P<.001) when compared with placebo. Beetroot juice did not influence resting or submaximal 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 NO₃^-on muscular performance is not known, and mechanistic studies and larger trials are needed to test this hypothesis.

Keywords: Aging; Exercise; Inorganic nitrate; Nitric oxide; Oxygen consumption.