L-Arginine and Traffic Pollution: A Targeted BP Signal

L-arginine may lower blood pressure during traffic-pollution exposure in adults who already have elevated blood pressure. In one randomized trial, 9 g per day for 14 days reduced systolic pressure by 5.3 mmHg at rest and by 7.5 to 9.9 mmHg during an outdoor walk, compared with placebo. That is a meaningful result—but it comes from one study, in one specific population, with no direct confirmation that nitric oxide caused the effect.

The more familiar use case, pre-workout performance, has fared worse. A 2025 crossover trial found that arginine briefly widened an artery after exercise in healthy young men but did not improve repetitions, volume load, fatigue, or plasma nitric oxide markers. Blood vessels can respond without your biceps getting the memo.

A blood-pressure signal during traffic exposure

In a 2021 randomized, double-blind, placebo-controlled crossover trial by Li et al., 118 Vancouver adults with systolic blood pressure of 120 to 159 mmHg took either 9 g of L-arginine daily or placebo for 14 days. They then completed a two-hour outdoor walk on a fixed route with measured traffic-related air-pollution exposure. Because the trial used a crossover design, participants could be compared under both supplement and placebo conditions.

After the walk, resting systolic blood pressure was 5.3 mmHg lower with arginine than with placebo (95% confidence interval [CI], −9.9 to −0.7). Diastolic pressure was 4.3 mmHg lower (95% CI, −7.2 to −1.3), and mean arterial pressure was 4.6 mmHg lower (95% CI, −7.9 to −1.3). The ambulatory readings recorded during the walk showed larger differences: systolic pressure was 7.5 to 9.9 mmHg lower, diastolic pressure 5.3 to 7.6 mmHg lower, and mean arterial pressure 4.7 to 7.9 mmHg lower than with placebo.

Those are blood-pressure measurements, not evidence that arginine prevented heart attacks, strokes, or pollution-related disease. Still, a 5 to 10 mmHg difference in an elevated-BP population is clinically relevant enough to take seriously. The study also described the regimen as safe and well tolerated over its 14-day duration, although it did not report specific gastrointestinal adverse-event rates, medication interaction data, or herpes simplex reactivation outcomes.

The nitric-oxide explanation fits—but remains unproven here

Arginine is the substrate for endothelial nitric oxide synthase, an enzyme that helps blood vessels relax. The appealing theory is that people with endothelial dysfunction have more asymmetric dimethylarginine, or ADMA, a molecule that competes with arginine at that enzyme. Extra arginine could improve the arginine-to-ADMA balance enough to restore nitric oxide production.

Human evidence supports ADMA as a plausible constraint on endothelial function. A cross-sectional study by Nolde et al. linked proton-pump inhibitor use with higher ADMA and impaired flow-mediated dilation, consistent with reduced activity of the ADMA-degrading enzyme DDAH. A 2023 study in people with chronic kidney disease also found that ADMA-related measures were associated with impaired peripheral microvascular function. These studies show associations in populations with vascular stress; neither tested arginine supplementation as an intervention.

Li et al. did not measure ADMA or flow-mediated dilation. More importantly, the trial found no significant change in plasma L-arginine–nitric oxide metabolites or inflammatory biomarkers. The blood-pressure result stands, but the proposed nitric-oxide pathway remains an inference rather than a demonstrated mechanism. Local vascular changes may escape a blood test, or another mechanism may explain part of the effect. The trial cannot settle that question.

Why the pre-workout story is different

A 2025 randomized, double-blind, placebo-controlled crossover study by Borges et al. tested arginine in 16 recreationally trained young men. Participants used an escalating four-day protocol: 3.2 g on day 1, 6.4 g on days 2 and 3, and 9.6 g on day 4. They then performed biceps curls at 65% of one-repetition maximum.

Arginine increased brachial artery dilation one minute after exercise versus placebo (p=0.023). Yet total repetitions did not differ significantly (p=0.305), and neither volume load nor fatigue ratio improved. Plasma nitric oxide also did not differ significantly (p=0.522). The study therefore separates a vascular response from a performance outcome: transient vasodilation did not translate into more work completed in this setting.

The result does not prove that arginine can never aid any form of exercise. The sample was small, the supplementation period lasted four days, and the test involved one resistance-exercise protocol. It does, however, directly challenge claims that an arginine-induced "pump" reliably increases reps or training volume in healthy young lifters.

A 2022 systematic review and meta-analysis of nitric-oxide-related food sources reaches a similarly restrained conclusion for endurance exercise. It pooled trials of dietary nitrate, polyphenols, L-arginine, and L-citrulline, so it cannot provide a clean arginine-only effect estimate. Even so, arginine did not emerge as a reliable ergogenic aid across the broader randomized evidence.

One promising pollution trial is not a standard protocol

Traffic pollution creates oxidative stress and can worsen vascular function, which makes an endothelial intervention biologically credible. But credibility is not replication. A 2024 systematic review of supplements studied against air-pollution toxicity found that this pre-exposure L-arginine approach was not an established, replicated intervention. We do not know whether the Li result applies to other cities, pollution mixtures, indoor exposure, people with normal blood pressure, or longer treatment periods.

L-citrulline deserves attention as a related but distinct option. It can raise circulating arginine through endogenous conversion while bypassing some first-pass hepatic clearance. A 2025 meta-analysis of 15 randomized trials and 415 middle-aged or older participants found that L-citrulline supplementation and watermelon intake reduced systolic blood pressure by 4.02 mmHg (95% CI, −6.54 to −1.50) and diastolic pressure by 2.54 mmHg (95% CI, −4.27 to −0.81). That evidence does not establish citrulline as a substitute for arginine against traffic pollution: the pollution-specific trial used L-arginine, not citrulline.

Who should care?

The evidence supports a narrow conclusion. L-arginine at 9 g daily for 14 days lowered measured blood pressure during traffic-pollution exposure in adults with elevated blood pressure in one well-designed crossover trial. It does not support L-arginine as a dependable resistance-training supplement for healthy young adults.

• Adults with elevated blood pressure and substantial traffic exposure have the most directly relevant evidence, though only from one trial.
• Healthy recreational lifters should not expect more repetitions or greater training volume from a short arginine protocol.
• People taking blood-pressure medicines, those with kidney disease, and anyone with recurrent herpes simplex should discuss high-dose arginine with a clinician before trying it. The trial does not answer interaction or herpes-risk questions.

Arginine has a credible vascular signal in a stressed cardiovascular setting. It has not earned a broad claim as either pollution armor or a performance enhancer.