This amino acid is essential to the human body for the production of serotonin, a brain chemical necessary for sleep and for mood regulation. Tryptophan is also the nutrient that the body uses to make melatonin. During the 1980's, however, tryptophan was widely available as a supplement in health food stores and other major retail outlets such as supermarkets and drug stores. Individuals used it for sleeping difficulties, premenstrual syndrome, stress, depression and alcohol and other drug abuse. Physicians in New Mexico and Minnesota had noted that persons with this unusual disease had all been taking tryptophan supplements.
Eosinophils are one of the blood components measured in a routine blood count.
A high eosinophil count is usually associated with a parasitic infection or severe allergy. EMS, however, produces an unusual cluster of symptoms. The CDC said that virtually all of these cases were linked to the use of tryptophan. EMS was virtually unknown in the United States before 1989, although tryptophan had been a popular nutrient for many years. These facts led to a search for a contaminant in certain batches of the nutrient rather than a problem with use of tryptophan as a nutritional supplement.