L-Lysine is an essential amino acid that the body cannot produce and thus must be ingested with the diet. L-Lysine creates a building block for protein and is important for normal growth and muscle turnover. It is also used to form carnitine, a substance found in most cells of the body. 

L-Lysine affects calcium transport in both the intestines and in the kidney. L-Lysine can enhance intestinal calcium absorption and improve the renal conservation of the absorbed calcium. Studies in animals have shown that dietary supplements with certain amino acids, particularly L-Lysine, can increase calcium absorption. A study in 30 women, 15 healthy and 15 with osteoporosis, found that supplementing with calcium and lysine reduced the loss of calcium in the urine. While the women given 3 grams of calcium alone had a progressive increase in calcium in their urine, the women who also received 400 mg of lysine lost less calcium through their urine. (1) This also suggests the potential usefulness of L-Lysine supplements for both preventive and therapeutic interventions in osteoporosis. Lysine may also play a part in controlling whereto calcium is transported in the body. For example, it has been shown to prevent the buildup of calcium in blood vessels in rats. (2) One test-tube study found that cells that were grown without lysine had an increased movement of calcium out of the cell but this increase did not occur in the cells that had Lysine present. (3)

L-Lysine may help reduce feelings of anxiety and the levels of the stress hormone. One study observed that L-Lysine blocked receptors involved in the stress response. Researchers found that L-Lysine blocked stress-induced fecal excretion and reduced the severity of diarrhea in a manner similar to the action of synthetic 5-HT4 receptor. (4) Another study has pointed to a combination of L-Lysine and L-Arginine as a potentially useful dietary intervention in otherwise healthy humans with high subjective levels of mental stress and anxiety. (5) L-Lysine can also be an effective therapy for improving negative and general psychopathology symptoms in chronic schizophrenia. (6) 

L-Lysine can also promote wound healing by helping create collagen. Lysine itself may act as a binding agent, thereby increasing the number of new cells at a wound and may promote the formation of new blood vessels. (7) Rabbits that received L-Lysine and L-Arginine had a 2-week reduced healing time compared to the control group. In another animal study, a combination of lysine and the amino acid arginine was able to speed up and improve the healing process of fractures. (8) 

Lysine is also good for eye health and can help to prevent diabetes, and high blood pressure. A study in rats with diabetes found that lysine supplements could prevent the development of cataracts. (9) Another study showed that lysine may help reduce blood sugar response in people with diabetes. Lysine ingestion resulted in a small decrease in glucose concentration. When lysine was ingested with glucose, the 2.5-h glucose area response decreased by 44%. (10) 

References: 

1. Civitelli R, Villareal DT, Agnusdei D, Nardi P, Avioli LV, Gennari C. Dietary L-lysine and calcium metabolism in humans. Nutrition. 1992 Nov-Dec; 8 (6): 400-5. 

2. Akihiro Shimomura, Isao Matsui, Takayuki Hamano, Takuya Ishimoto, Yumiko Katou, Kenji Takehana, Kazunori Inoue, Yasuo Kusunoki, Daisuke Mori, Chikako Nakano, Yoshitsugu Obi, Naohiko Fujii, Yoshitsugu Takabatake, Takayoshi Nakano, Yoshiharu Tsubakihara, Yoshitaka Isaka, Hiromi Rakugi Dietary L-Lysine Prevents Arterial Calcification in Adenine-Induced Uremic Rats J Am Soc Nephrol. 2014 Sep; 25 (9): 1954–1965. 

3. Civitelli R, Fedde KN, Harter J, Halstead LR, Gennari C, Avioli LV. Effect of L-lysine on cytosolic calcium homeostasis in cultured human normal fibroblasts. Calcif Tissue Int. 1989 Sep; 45 (3): 193-7. 

4. Miro Smriga, Kunio Torii. L-Lysine acts like a partial serotonin receptor 4 antagonist and inhibits serotonin-mediated intestinal pathologies and anxiety in rats Proc Natl Acad Sci U S A. 2003 Dec 23; 100 (26): 15370–15375. 

5. Smriga M, Ando T, Akutsu M, Furukawa Y, Miwa K, Morinaga Y. Oral treatment with L-lysine and L-arginine reduces anxiety and basal cortisol levels in healthy humans. Biomed Res. 2007 Apr; 28 (2): 85-90. 

6. Zeinoddini A, Ahadi M, Farokhnia M, Rezaei F, Tabrizi M, Akhondzadeh S. L-lysine as an adjunct to risperidone in patients with chronic schizophrenia: a double-blind, placebo-controlled, randomized trial. J Psychiatr Res. 2014 Dec; 59: 125-31. 

7. Debatosh Datta, Akshay Bhinge, Vidya Chandran. Lysine: Is it worth more? Cytotechnology. 2001 Jul; 36 (1-3): 3–32. 

8. Shivam Sinha, Satish Chandra Goel. Effect of amino acids lysine and arginine on fracture healing in rabbits: A radiological and histomorphological analysis Indian J Orthop. 2009 Oct-Dec; 43 (4): 328–334. 

9. Sulochana KN, Punitham R, Ramakrishnan S. Beneficial effect of lysine and amino acids on cataractogenesis in experimental diabetes through possible antiglycation of lens proteins. Exp Eye Res. 1998 Nov; 67 (5): 597-601. 

10. Kalogeropoulou D, LaFave L, Schweim K, Gannon MC, Nuttall FQ. Lysine ingestion markedly attenuates the glucose response to ingested glucose without a change in insulin response. Am J Clin Nutr. 2009 Aug; 90 (2): 314-20.