L-lysine is an essential amino acid that is important for many biological functions, such as immunity, energy production and muscle growth. Since it is naturally abundant in high protein foods such as meat, eggs, beans and legumes, those most likely to suffer from deficiency are vegetarians or vegans who consume a diet low in legumes and high in grain-based foods.
One of the most common uses for supplemental L-lysine is for preventing cold sores caused by the Herpes Simplex virus. It does this in three different ways: by preventing infection with the virus, reducing the risk of developing cold sores in those with the virus and speeding up the recovery after cold sores develop. Lysine inhibits replication of the herpes virus that causes the visible outbreaks and pain, itching and sores around the lips. It interferes with the absorption of the amino acid arginine, which the herpes virus uses to replicate. Without arginine, the virus cannot be fully functional which allows the body to heal quicker and reduce the possibility of recurrence.
Lysine also supports bodybuilding and muscle growth and helps maintain carnitine levels, an important factor in energy and aging. Lysine supports bone health by ensuring the proper absorption of calcium and helping to form collagen that makes up bone cartilage and connective tissues. Finally, supplementation with lysine has been shown to reduce mood imbalances and even cortisol levels in those who consume low amounts of lysine.