L-Lysine is an essential amino acid needed for growth and to help maintain nitrogen balance in the body. Essential amino acids like L-Lysine can not be made in the body and must be supplied by the diet or supplements. L-Lysine supplementation increases the absorption of calcium and may reduce its excretion. As a result some researchers believe that l-lysine may eventually be shown to have a role in the prevention and treatment of osteoporosis. L-Lysine has many functions in the body because it is incorporated into many proteins, each of which is used by the body for a variety of purposes. L-Lysine interferes with replication of herpes viruses and is therefore often prescribed by nutritionally oriented doctors to people with cold sores or genital herpes.