EAST LANSING, Mich. — The rare blood disorder linked to the dietary supplement L-tryptophan appears to be caused by impurities found in the supplements, and immune-system weaknesses that make some individuals more susceptible to the illness, federal health officials said Wednesday.
The officials said they found chemical contaminants in all of the L-tryptophan samples they studied. Any of the dozens of impurities could have played a role in the illness, they added.
About 1,550 cases of esinophilia-myalgia syndrome, or EMF, have been reported in the United States since November, 1989, according to the U.S. Centers for Disease Control. The disorder causes a vast array of symptoms including breathing problems, cough, muscle pain, swelling of the extremities, fever and rash. Twenty-four deaths have been reported.
"A lot of people were taking L-tryptophan for years, but they were getting sick in 1989. This suggests there is something different about the product on the market in 1989," Dr. Leslie Swygert of the CDC said Wednesday at an international conference on Issues in Food Safety and Toxicology at Michigan State University.
But, she said: "There is probably variation in susceptibility. It could be a predisposition people are born with or something environmental that triggers it."
L-tryptophan is an amino acid, a protein essential to the body, found naturally in some foods. It was also sold over the counter as a remedy for premenstrual syndrome, depression, stress reduction, insomnia and hyperactivity in children.
The Food and Drug Administration issued a partial recall of the product last November after the outbreak of EMF was linked to the supplement. The recall was expanded in March to include even small doses of L-tryptophan.
Although a majority of cases of EMF have been linked to consumption of L-tryptophan manufactured by a single Japanese company, impurities have been found in samples from all manufacturers of the dietary supplement, the experts said Wednesday. Officials have been frustrated in their attempts to identify which, if any, contaminant is involved, said Douglas Archer of the FDA.
"There are contaminants in all the preparations of L-tryptophan we have looked at," Archer said. "The impurities from all the sources are there in very, very small amounts. That's a puzzle. If a contaminant is somehow triggering EMF, it must be a very potent substance or an irreversible substance so that damage accumulates and can't be repaired.
"There is a long way to go to identify what these chemicals are."
Archer said the FDA would resist pressure to allow some manufacturers to return their L-tryptophan formulations to the market. "Probably the bulk of the pressure on the agency right now is to bring the substance back on the market," he said.
"We don't believe that would be prudent. We don't think it makes any sense to let a substance back that has been linked to a serious and life-threatening disorder without knowing what happened--what went wrong."
EMF is characterized by a high number of white blood cells called esinophils in the blood stream. Esinophils are important in defending against infection in the body, but can also become toxic and attack muscles and other tissues. Contaminants in L-tryptophan, other drug substances or a combination of both might cause the body to make more esinophils, triggering the disease.