Tryptophan produced by Showa Denko and epidemic eosinophilia-myalgia syndrome.
Level 5 - mechanism / opinion, no new human data
Narrative review and commentary synthesizing observational case-control studies without systematic review methodology
What was done
Review of epidemiological and observational evidence—evaluating Bradford Hill criteria—from multiple independent case-control studies examining the association between L-tryptophan manufactured by Showa Denko KK and the 1989 epidemic of eosinophilia-myalgia syndrome (EMS) in the United States.
What was found
No numerical estimates, confidence intervals, or exact p-values were reported in the abstract. Exposure to L-tryptophan was reported as essentially universal among cases and rare among controls. Among six L-tryptophan manufacturers, only Showa Denko KK product was associated with illness. The abstract reports a dose-response relationship with the amount consumed and notes that EMS incidence diminished abruptly after product recall.
Why it matters
This review synthesizes the epidemiological case that contaminated L-tryptophan from a single manufacturer caused the 1989 US EMS outbreak, highlighting supplement surveillance and manufacturing safety.
Limits
The abstract provides narrative conclusions without quantitative effect estimates, confidence intervals, or exact sample sizes. It synthesizes observational case-control studies rather than experimental data and does not specify the chemical contaminant in the abstract.
Cited by
- supports Contaminated tryptophan batches originating from Japan caused severe illness and death, leading to a long-term ban on its sale.