TRYPTOPHAN PRODUCED BY SHOWA-DENKO AND EPIDEMIC EOSINOPHILIA-MYALGIA-SYNDROME

Evidence from an array of scientific studies strongly supports the con clusion that ingestion of products containing L-tryptophan (LT) produc ed by Showa Denko KK caused the 1989 epidemic of eosinophilia-myalgia syndrome (EMS) in the United States. In case-control studies of EMS, L T exposure was essentially universal among cases but rare among contro ls. Of 6 manufacturers of LT, only LT manufactured by Showa Denko KK w as clearly associated with illness. The data meet other Kill criteria for inferring a causal relationship. Consistent findings were found in multiple independently conducted studies, There was a dose-response e ffect, with risk of illness increasing as a function of the amount of tryptophan consumed. The extremely small p values observed in the mult iple independently conducted studies effectively rule out the possibil ity that the tryptophan-EMS association was the result of chance. More over, no potential confounding factor or bias explains the association . The incidence of EMS in the United States diminished abruptly once L T containing products were recalled.