L-arginine supplementation to mitigate cardiovascular effects of walking outside in the context of traffic-related air pollution in participants with elevated blood pressure: A randomized, double-blind, placebo-controlled trial

Exposure to traffic-related air pollution (TRAP) increases blood pressure (BP) and cardiovascular morbidity and mortality. We aimed to evaluate the potential efficacy of L-arginine supplementation in mitigating the adverse cardiovascular effects of adults with elevated BP walking outside under TRAP using a randomized, double-blind and placebo-controlled trial. 118 adults with elevated BP were recruited and were randomly assigned to either the placebo group or the intervention group with 9 g/day L-arginine supplementation for 2 weeks. On the 14th day, paired participants from the two groups walked along a traffic road for 2 h. Resting BP, L-arginine-nitric oxide metabolites and inflammatory biomarkers were measured before, during and after the 2 h exposure scenario, and ambulatory BP and Holter were measured during the 2 h outdoor walk. Participants in the intervention group had significantly elevated plasma L-arginine levels compared to the placebo group after supplementation. The two groups had similar exposures to traffic-related air pollutants. However, participants in the intervention group showed significant reductions of 5.3 mmHg (95% CI: -9.9, -0.7) in resting systolic BP (SBP), 4.3 mmHg (95% CI: -7.2, -1.3) in resting diastolic BP (DBP) and 4.6 mmHg (95% CI: -7.9, -1.3) in resting mean arterial pressure (MAP) at 30 min after the 2 h outdoor walk compared with the placebo group. There were also significant decreases in ambulatory SBP, DBP and MAP (7.5-9.9 mmHg, 5.3-7.6 mmHg and 4.7-7.9 mmHg, respectively) during the walk in the intervention group compared with the placebo group. There were no substantial changes in ST-segment level, L-arginine-NO metabolites and inflammatory biomarkers, and no significant associations were found between specific traffic-related air pollutants and cardiovascular health indicators. Specifically, our study shows that oral L-arginine supplementation was safe and well-tolerated, and could improve BP levels in adults with elevated BP during outside walk under TRAP.