MONDAY, Jan. 5 (HealthDay News) -- Headache frequency and severity caused by traumatic brain injury might signal cognitive deficits, suggests a new study of Iraq war veterans.

Traumatic brain injuries, also called concussions, are common among veterans who served in Iraq. And as deployment times have become longer, military personnel have more chances to be exposed to explosions that can cause injury.

"The most important finding was that the soldiers who continued to have problems with headaches and PTSD [post-traumatic stress disorder] were much more likely to have signs of residual cognition impairment or abnormalities," said study author Dr. Robert L. Ruff, professor of neurology at Case Western Reserve University and neurology service chief at the Louis Stokes Cleveland Veterans Affairs Medical Center. "By themselves, the deficits were not severe, but they compromised the veterans' ability to return to where they were."

The researchers studied 126 veterans who had lost consciousness from blasts and explosions an average of three times while in Iraq, none for more than 30 minutes. Neurological and neuropsychological testing revealed impairments in 80 of the veterans that the researchers attributed to concussions. Those veterans had been exposed to more explosions than the others, the study found.

Among veterans who had brain impairments, 93 percent reported having headaches, compared with 13 percent of those who showed no dysfunction on the neurological tests.

Their headaches also were more severe and persistent. Veterans with no brain impairments all described having tension-like headaches about four times a month, whereas 60 percent of those with brain impairments resulting from their concussions described migraine-like headaches that occurred an average of 12 times a month.

In addition to more frequent and severe headaches, many of the veterans also experienced other PTSD symptoms, including sleep disorders and problems with their sense of smell, the study found.

"The olfactory nerves are very small, so when there's movement, they get sheared off," said Keith Young, associate professor and vice chairman for research at Texas A&M Health Science Center College of Medicine in College Station, Texas, who also works with the VA Center of Excellence for Research on Returning War Veterans.

"People who have multiple exposures to blasts that cause loss of consciousness need to be carefully monitored for potential problems in the future," Young said.