Arginine, also called L-arginine, is an amino acid used by the body as a protein building block. It’s also an intermediate metabolite in the urea cycle and the nitric oxide cycle. The urea cycle removes excess ammonia, a toxic molecule, from the body, and the nitric oxide cycle produces nitric oxide, which is an important signaling molecule involved in vascular function. Although the body can synthesize arginine, it can also be obtained in the diet through protein-containing foods or dietary supplements.
Daily supplementation with arginine can reduce blood pressure in people with healthy blood pressure and people with hypertension (high blood pressure). Evidence also supports the use of arginine to help improve birth outcomes in pregnant women with conditions like hypertension and preeclampsia or a history of poor pregnancy outcomes. This includes reducing the risk of infants small for gestational age and intrauterine growth restriction of the baby. Arginine can also improve maternal outcomes by reducing the risk of preeclampsia in the pregnant mother. Additionally, arginine can reduce blood triglycerides, particularly in people older than 50 or in people with metabolic syndrome or type 2 diabetes.
In men with erectile dysfunction, daily supplementation with arginine can alleviate symptoms. Furthermore, the combination of arginine with phosphodiesterase type 5 inhibitors (PDE5Is), like Viagra, improves sexual function in men with erectile dysfunction more than treatment with PDE5Is alone.
Evidence also shows that daily supplementation with arginine might increase VO2max, but the magnitude of improvement is negligible and unlikely to be clinically meaningful. Furthermore, most studies find no beneficial effect of arginine on exercise performance. It is only when highly-varied types of exercise (aerobic, anaerobic, resistance, etc.) and performance outcomes (time-to-exhaustion, time-trials, sprint time, 1-rep-max, reps-to-failure, etc.) are inappropriately pooled that meta-analyses find a performance benefit from arginine.
Animal studies show that neither oral nor intravenous delivery of arginine causes toxicity, even at high doses. However, supplementation with arginine has been reported to cause adverse gastrointestinal effects in humans, including nausea, vomiting, and diarrhea. For this reason, upper limit guidelines of approximately 20 to 30 grams per day have been proposed for supplemental arginine intake, but more long-term safety data in humans are needed to accurately define a tolerable upper intake level.
Nitric oxide is a key molecule involved in vasodilation, i.e., the relaxation and widening of blood vessels to increase blood flow to tissues that lack oxygen or nutrients. The beneficial effects of arginine on high blood pressure and erectile dysfunction are likely related to vasodilation because arginine increases nitric oxide synthesis.
A similar mechanism may explain how arginine might increase VO2max. Additionally, nitric oxide might have direct effects on muscle contractile function. Furthermore, arginine’s role in the urea cycle helps with ammonia excretion, the accumulation of which might induce fatigue during exercise.
The standard preworkout dose for arginine is 3–6 grams.
Taking more than 10 grams of arginine at once can result in gastrointestinal distress and diarrhea, but it is possible to maintain elevated arginine levels throughout the day by taking three spaced doses (15–18 grams/day). However, citrulline supplementation is more effective at maintaining elevated arginine levels for long periods of time.
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