There has been much research performed surrounding dietary nitrate supplementation in young, healthy, and athletic populations, especially in the form of acute beetroot juice consumption(1). However, chronic supplementation in an age-varied population has remained a largely neglected field. This study supplemented healthy participants (aged 24-86 years) with two beetroot extract pills per day (~600 mg of beetroot extract, ~2.8-3.0 mg nitrate) for 12-months (n=42). At baseline, three, six, nine, and twelve-months the participants took part in a suite of tests to assess muscle mass, size, and strength outcomes. Bioimpedance analysis was used to assess skeletal muscle mass (SMM) and an ultrasound measurement of the lateral head of the gastrocnemius was used to report muscle thickness (MT). Handgrip strength (HGS) and a knee extension (KE)/flexion (KF) protocol (concentric–concentric at 60°/s) were used to assess isometric and isokinetic strength, respectively. Following the chronic supplementation period no changes in SMM (p=0.103) or MT (p=0.0684) were observed at any time-point. However, all mean muscle strength outcomes improved by 3-months compared to baseline (HGS 1.09 ± SD 2.19 Kg (p=0.028), KE 15.12 ± SD 23.65 Kg (p=0.003), KF 5.82 ± SD 10.54 Kg (p=0.008)). Furthermore, the improvements in HGS and KF demonstrated continued improvement as the supplementation period progressed (12 months: HGS 2.03 ± SD 2.80 Kg (p=0.002), KF 12.71± SD 14.98 Kg (p<0.0001).
A subgroup analysis was also undertaken to observe if the efficacy of supplementation was affected by age. The participants were split into two subgroups, ‘Young’ (aged 24-59 years, n=31) and ‘Older’ (aged 60+ years, n=11). The ‘Older’ sub-group demonstrated no statistically significant improvement in isometric or isokinetic strength at any point during the supplementation period, whereas the ‘Young’ sub-group demonstrated significant improvements in all strength outcomes (HGS p=0.017, KE p=0.019, KF p<0.0001), perhaps suggesting that beetroot supplementation is more effective at improving muscle strength in a younger population.
Overall, these findings suggest that strength increases post-supplementation cannot be attributed to an increase in muscle mass or volume, but improved muscle quality and physiological efficiency, as in agreement with the recent literature(2). Interestingly, the beetroot extract used in this study has relatively little nitrate content (~2.8-3.0 mg) compared to previous beetroot juice supplementation studies(3, 4), suggesting that nitrate may not be the key driver of the effects observed in this study. To corroborate these findings a larger, powered study would be required, ideally with the inclusion of a placebo or no intervention group.
Ethical approval for this study was obtained from the London-Brighton and Sussex Research Ethics Committee (REC Ref: 22/PR/1028).