Threonine is an essential amino acid, meaning that the human body cannot produce it and must obtain it from food sources. It plays a crucial role in protein synthesis and is important for the production of various proteins, including those involved in immune function and muscle health. Foods rich in threonine include dairy products, meat, fish, and certain grains. In addition to its role in protein formation, threonine is involved in the production of collagen and elastin, which are vital for skin and connective tissue health. It also contributes to the synthesis of neurotransmitters, supporting overall brain function and mood regulation.