Melatonin: An Overview on the Synthesis Processes and on Its Multiple Bioactive Roles Played in Animals and Humans

Melatonin is a natural hormone synthesized mainly by the pineal gland of vertebrates, and, secondarily, by other tissues and organs as well. It is deemed a bioactive molecule due to the multiple roles and functions it performs in animals and humans. Research conducted up to 2024 has reported the presence of melatonin in a wide variety of plants and bacteria, as well. This review aims to collect some of the scientific data to identify and describe the main sources of melatonin, and to document the functions and roles it plays in animal organisms. It also includes a description of the main technological and nutritional factors that can positively or negatively influence the synthesis and secretion process of melatonin, which is subsequently transported from the animal body into some food products, such as milk. This paper also includes information on the interaction between melatonin and other bioactive compounds present in animal and human bodies, with the aim of identifying what other functions and roles this hormone performs, and whether it interacts with other substances present in the vertebrate organism.