As one of the eight essential amino acids L-threonine is considered critical to the proper functioning of the human body. Because L-threonine is not as plentiful in our normal foods as some other amino acids, individuals who are on very strict diets are sometimes prescribed supplements to ensure they have enough L-threonine in their systems. Vegetarians are also common users of this supplement due to the fact that their dietary choices restrict their intake of this necessary amino acid. 

Threonine helps keep connective tissues and muscles throughout the body strong and elastic, including the heart, where it is found in significant amounts. It also helps build strong bones and tooth enamel, and may speed wound healing or recovery from injury.