L-Arginine is one of many amino acids the body needs to function regularly. Like other amino acids, L-Arginine plays a vital role in building protein. Dietary proteins represent key nutrients for bone health and thereby function in the prevention of osteoporosis. (1) L-Arginine helps the body to eliminate ammonia (a waste product) and stimulates the release of insulin. The body uses L-Arginine to produce nitric oxide, a compound that relaxes the blood vessels. Nitric oxide helps blood vessels to ease and expand and is important for regulating your blood flow.

In humans, L-Arginine induces growth hormone release, via a decrease in somatostatinergic tone. (2) Studies have shown that resting growth hormone responses increase with oral ingestion of L-Arginine in a dosage range of 5-9 g arginine. (3) Most studies using oral arginine have shown that arginine alone increases the resting growth hormone levels by at least 100%. Another study, reported in Biology of Sport, found that taking arginine supplements before exercise increased the time it took for male wrestlers to become exhausted. (4) 

The Asia Pacific Journal of Clinical Nutrition suggests that arginine supplements may have positive effects on your immune system. (5) Arginine helps in wound healing, supports recovery from surgery and, fights infections. A study has shown that L-Arginine enhances wound healing and T-cell-mediated immune function in rodents. (6) A study with 36 healthy, nonsmoking human volunteers indicated that L-Arginine supplementation significantly enhances the amount of collagen deposited into a standardized wound as assessed by the amount of hydroxyproline present. (7) 

L-Arginine also plays an important role in brain health. L-Arginine is involved in diverse physiological and pathological processes, including neurotransmission, neurogenesis and neuroplasticity, cellular redox metabolism and redox stress, inflammation, and regulation of cerebral blood flow. (8) L-Arginine can help treat Alzheimer's disease, the most common degenerative brain disease that causes dementia. 

Some research suggests that arginine supplements may help improve blood flow. (9) As a consequence doctors sometimes prescribe arginine supplements to treat erectile dysfunction (ED). In fact, early studies have found that arginine supplements may help alleviate ED in men with low nitrate levels. A study reported in Urology demonstrated that oral supplements of L-Citrulline may help treat mild to moderate ED. (10) 

L-Arginine supplements may also have benefits for people with certain cardiovascular conditions such as coronary artery disease, clogged arteries, and angina. (9) More research is needed, but it appears to have the potential for treating diabetes. A study reported in Endocrinology found that arginine supplements can help improve glucose tolerance in mice and this suggests that L-Arginine is helpful in treating diabetes.

References: 

1. Bonjour JP. Protein intake and bone health. Int J Vitam Nutr Res. 2011 Mar; 81 (2-3): 134-42. 

2. Cochard A, Guilhermet R, Bonneau M. Effects of arginine, growth hormone-releasing hormone (GHRH) and neostigmine administered singly or in paired combinations on growth hormone (GH) release in pigs. Reprod Nutr Dev. 1997 Sep-Oct; 37 (5): 589-98. 

3. Kanaley JA. Growth hormone, arginine and exercise. Curr Opin Clin Nutr Metab Care. 2008 Jan; 11 (1): 50-4. 

4. Yavuz HU, Turnagol H, Demirel AH. Pre-exercise arginine supplementation increases time to exhaustion in elite male wrestlers. Biol Sport. 2014 Aug; 31 (3): 187-91. 

5. Kang K, Shu XL, Zhong JX, Yu TT. Effect of L-arginine on immune function: a meta-analysis. Asia Pac J Clin Nutr. 2014; 23 (3): 351-9. 

6. Stechmiller JK, Childress B, Cowan L. Arginine supplementation and wound healing. Nutr Clin Pract. 2005 Feb; 20 (1): 52-61. 

7. Barbul A, Lazarou SA, Efron DT, Wasserkrug HL, Efron G. Arginine enhances wound healing and lymphocyte immune responses in humans. Surgery. 1990 Aug; 108 (2): 331-6; discussion 336-7. 

8. Jing Yi, Laura L. Horky, Avi L. Friedlich, Ying Shi, Jack T. Rogers, Xudong Huang. L-Arginine and Alzheimer's Disease Int J Clin Exp Pathol. 2009; 2 (3): 211–238. 

9. L-arginine, Mayo Clinic. 2017 Oct;10. Cormio L, De Siati M, Lorusso F, Selvaggio O, Mirabella L, Sanguedolce F, Carrieri G. Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction. Urology. 2011 Jan; 77 (1): 119-22.