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.