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L-Arginine is a semi-essential amino acid that is known as the precursor for the endogenous synthesis of nitric oxide (NO) [1; 2], and is known to possess strong immune modulation properties .
Mechanisms of action
One mechanism L-Arginine contributes to is the removal of excess ammonia from the body, including the formation of muscle protein, amino acids and creatine . ~40% of dietary L-arginine is broken down by the intestine before entering the circulation 
Benefits of L-Arginine
L-arginine and weight loss
Supplementing animals with L-arginine over a 60-day period showed a decrease in in body fat growth in growing pigs . Authors of these results reported the novelty in using L-arginine in treating obesity in humans. Another study documented L-arginine’s effect on a diet-induced obesity rat model .
L-arginine and blood pressure
An L-arginine enriched diet, using both natural foods or pharmacologic preparation, was administered to six healthy individuals, and results showed that L-arginine was able to decrease blood pressure in the subjects .
L-arginine in its effect on insulin sensitivity in obese individuals showed a lowering of systolic and diastolic blood pressure after administration of 8.3g/day of L-arginine over 21 days .
A double-blind placebo-controlled study assessing a high-dose (5g/day) L-arginine on men with erectile dysfunction showed significant subjective improvements in sexual function . Another similar study, using a randomised clinical trial setting, was conducted evaluating efficacy and safety of 6g L-arginine glutamate for treatment of erectile dysfunction (ED) .
L-arginine and pregnancy
In a study seeking to determine the effects of an L-arginine supplementation, 228 women were administered L-arginine and results were positive in showing that L-arginine reduced incidences of pre-eclampsia in a high-risk population .
L-arginine body building and exercise
In one study, L-arginine along with creatine improved the number of repetitions performed on a bench press exercise . In 8 healthy patients, L-arginine significantly decreased exercise-induced peak plasma ammonia and lactate .
L-arginine and sleep
One interesting study looked at overnight plasma NO levels in sleep apnoea patients and how treatment with nasal continuous positive airway pressure (nCPAP) affected the day after L-arginine levels . After treatment, all patients were recorded as having significant increases of L-arginine. Remarkably, results suggested the importance of Nitric oxide (NO) in sleep apnoea .
Side effects vary from nausea and diarrhea – from single large doses of L-arginine -, to no side effects at all [26; 2].
High doses of L-arginine – 30g – have reported hypertension with tachycardia, along with an increase in cardiac output . In addition, anaphylaxis might also be a side effect from L-arginine supplementation; in this regard, those taking L-arginine should reconsider if suffering from allergic tendencies .
3-6 grams L-arginine is considered a safe dose . Majority of side effects from L-arginine have been reported at doses exceeding 9 grams – when taken as part of daily dose regime of >30d per day L-arginine . Highest L-arginine dose recorded was 42g/day for 6 weeks in patients suffering from cystic fibrosis, with no adverse effects reported . Table 2 describes some L-arginine doses relative to individual studies.