Effects of dietary nitrate supplementation on the oxygen cost of exercise and walking performance in individuals with type 2 diabetes: A randomised, double blind, placebo-controlled cross-over trial.

BACKGROUND: Dietary nitrate supplementation has been shown to reduce the oxygen (O2) cost of exercise and enhance exercise tolerance in healthy individuals. This study assessed whether similar effects could be observed in individuals with type 2 diabetes (T2DM). METHODS: In a randomised, double blind, placebo-controlled cross-over study, 48 participants with T2DM supplemented their diet for four days with either nitrate rich beetroot juice (70ml/day, 6.43mmol nitrate/day) or nitrate depleted beetroot juice as placebo (70ml/day, 0.07mmol nitrate/day). After each intervention period, resting plasma nitrate and nitrite concentrations were measured subsequent to participants completing moderate-paced walking. Pulmonary gas exchange was measured to assess the O2 cost of walking. Following a rest period, participants performed the six-minute walk test (6MWT). RESULTS: Relative to placebo, beetroot juice resulted in a significant increase in plasma nitrate (placebo: 57±66 vs. beetroot: 319±110µM; P <0.001) and plasma nitrite concentration (placebo: 680±256 vs. beetroot: 1065±607nM; P <0.001). There were no differences between placebo juice vs. beetroot juice for the O2 cost of walking (946±221 vs. 939±223ml.min(-1), respectively; P =0.59), and distance covered in the 6MWT (550±83 vs. 554±90m, respectively; P =0.17). CONCLUSION: Nitrate supplementation did not affect the O2 cost of moderate-paced walking or improve performance in the 6MWT. These findings indicate that dietary nitrate supplementation does not modulate the response to exercise in individuals with T2DM. TRAIL REGISTRATION: ClinicalTrials.gov NCT02206074 FUNDING: Diabetes UK.