Lead author Rakib Rayhan of Georgetown University in Washington said the same patterns found using brain scans and exercise stress tests were not detected in the control group of healthy subjects, the Chicago Tribune reported.
After the 1991 Gulf War, veterans complained of various symptoms including pain, fatigue, headaches and cognitive impairment. It affects some 30 percent of the nearly 700,000 troops who served in the war.
Numerous studied were conducted on exposure to nerve agents, pesticides, radiation and smoke from burning oil wells but no definitive cause for Gulf War illness was identified.
In one group of 18 veterans, pain levels were elevated after exercise and their brain scans showed a loss of brain matter in the regions associated with pain regulation.
In another group of 10 veterans, exercise triggered a condition in which moving from lying down to a standing position causes the heart to race. This group had atrophy in the brainstem, which controls heart rate and blood pressure, the study said.
The study was published in the journal Plos One.