It’s an amino acid, which means it serves as a building block for proteins. Since it is not produced by the body, it’s considered an essential amino acid; you need to ensure sufficient intake through food or supplements. Lysine may support healthy, strong bones, which are less likely to weaken or break. It may promote the absorption of calcium, which is the mineral mainly responsible for building bone mass, as well as supporting strong teeth. At the same time, it can decrease the amount of calcium that is excreted from the body, and it encourages increased bone-building activity in the cells, including the collagen-building cells. L-lysine may boost immunity by helping maintain healthy gum and lip tissues, which are areas where viruses or bacteria may be able to enter the body, so keeping them strong may prevent you from getting sick. It may also help decrease feelings of mild anxiety.