ABSTRACT
Sleep, although much sought after, is sometimes not easily achieved. A glass of warm milk taken at bedtime is probably one of the oldest sleep aids known, and its use by millions of people over hundreds of years testifies to its effectiveness. Thus, in 1965, when it was realized that the brain chemical serotonin played an important role in the regulation of sleep, it seemed possible that L-tryptophan, a precursor of serotonin, might function as a useful sedative.1 Because casein, which makes up about 3 percent of cow's milk, consists of about 1.2 percent of L-tryptophan, the presence of that amino acid was thought to explain the beneficial effects of milk in treating insomnia.
