Exposure to pesticides and other chemicals may be causing the chronic fatigue, severe muscle pain, memory loss and other illnesses experienced by about 250,000 Persian Gulf War veterans, a new research showed.

“Convergent evidence now strongly links a class of chemicals – acetylcholinesterase inhibitors – to illness in Gulf War veterans,” Dr. Beatrice Golomb of the University of California, San Diego, lead author of the study said in e-mailed comments, according to Reuters.

This is the first research to link soldiers’ symptoms to chemical exposure. For many years, U.S. officials contended that Gulf War symptoms were caused by psychological stress. The new research revealed that nearly 30 percent of troops who took part in the brief war have reported symptoms that include fatigue, memory loss, pain, and difficulty sleeping.

Dr. Golomb reviewed more than 70 studies on Gulf War syndrome and acetylcholinesterase inhibitors including the anti-nerve gas pyridostigmine bromide, or PB, given to troops at the time; pesticides used aggressively to control sand flies; and the nerve gas sarin.

She found that 18 of the 21 epidemiological studies looking at chronic health problems in Gulf War veterans showed a connection to at least one kind of acetylcholinesterase inhibitor exposure.

Acetylcholinesterase inhibitors, or AChEis, act in the body to blunt the effect of an enzyme that regulates a brain chemical called acetylcholine. That substance helps neurons to fire. When the enzyme that regulates this chemical is blocked by an inhibitor, it causes the neurons to fire excessively, Golomb says.

“This leads to uncontrolled muscle action, including of muscles involved in breathing, and can prevent people from breathing. It also causes abnormal brain function. That’s why nerve gas is a bad thing to be exposed,” Golomb said in the review.

Exposure to AChEIs could also be linked to the higher rate of amyotrophic lateral sclerosis (ALS), or Lou Gehrig’s disease, in Gulf War veterans. Sporadic ALS has been associated with exposure to agricultural chemicals. Moreover, men and women with the Gulf War symptoms were more likely to have lower concentrations and activity levels of enzymes, which work to clear AChEIs from the system. Genetics may affect the way the body processes these chemicals, specifically the actions of these related enzymes.

“They’re giving certain people so many of these nerve agent pills or pesticides, and [the authors] say that some people metabolize them and some not. Are we really giving a toxic dose apart from the genetics? What are they giving and have they really tested the amounts that they’re giving? Are we overdosing?” said Joy Ray Miller, and assistant professor of pharmacy practice at the Irma Lerma Rangel College of Pharmacy at Texas A&M Health Science Center, according to the Washington Post.

Officials for the Pentagon and the Department of Veterans Affairs did not return calls seeking comment on Golomb's new report.

Dr. Golomb’s findings appeared Monday in Proceedings of the National Academy Sciences.