Sleep patterns are controlled by the hormone melatonin. In turn, melatonin is synthesised from serotonin, a metabolite of the amino acid L-tryptophan. Dietary sources of L-tryptophan increase plasma levels of the amino acid and cause increased uptake to the brain. In the brain the L-tryptophan is converted to serotonin and then to melatonin and this induces sleep. Foods high in L-tryptophan therefore stimulate sleep. Edam cheese is particularly good source of L-tryptophan and can improve sleep quality if eaten just before bed.