(HealthDay) -- Lingering symptoms from combat-related traumatic brain injuries -- even "mild" cases -- may persist for years, according to a new study of U.S. veterans who served in Iraq and Afghanistan.
Veterans were still battling headaches, depression, dizziness and other symptoms up to eight years after their head injury occurred, researchers found.
The study looked at 500 veterans who underwent general health and depression screenings between 2008 and 2011 at the Oklahoma City VA Medical Center and were found to have symptoms of mild traumatic brain injury and post-concussion syndrome.
The participants, mostly men, were grouped according to whether their head injury had occurred within the previous two years, three to four years, five to six years, or seven to eight years.
The patients self-rated six symptoms: headache, dizziness, balance problems, poor coordination, difficulty with decisions, and depression.
Whether the injury had occurred two years or eight years earlier made no significant difference in frequency or intensity of symptoms. And the type of injury made no difference.
"There was a tendency for depression to be a bit more common in the five-to-eight [year] group," said study author Dr. James Couch, a professor of neurology at the University of Oklahoma Health Sciences Center in Oklahoma City. "So not only does this not go away, which is what we figured we would probably find -- it may tend to get worse."
Traumatic brain injury is considered a hallmark combat injury.
"About two-thirds of the people had primarily blast injuries, and about one-third had injuries related to falls, motor vehicle accidents, and so forth," Couch said. "One of my patients had a rocket hit a balcony right above him, and he was knocked out by the falling pieces of concrete."
Study cases fell on the lower end of the trauma spectrum.
"These are basically mild traumatic brain injuries," Couch said. "'Mild' meaning that that patient did not have lacerations that were severe, did not have a skull fracture, did not require surgery on the head because of the injury."
One expert described the prevalence of mild traumatic brain injury.
"Probably 10 percent to possibly over 20 percent of deployed service members develop [traumatic brain injury]," said Dr. Steven Cohen, a professor of anesthesiology and critical care medicine at the Johns Hopkins University School of Medicine and a colonel in the U.S. Army Reserves. "Amongst those diagnosed with [traumatic brain injury], 40 percent to 50 percent are mild."
Both experts said the persistence of side effects seen in the study is discouraging.
"With almost any medical condition, the longer you have it, the less likely it is that it will ever go away," said Cohen, who works with patients at the Walter Reed National Military Medical Center in Bethesda, Md.
"One good thing: Now the military does a very good job of screening people and getting them treatment," Cohen said. "They all have case managers; they have wounded-warrior centers. I think it's more difficult in reservists and people with mild injuries. Because they end up leaving active duty and they don't have the same support system."
Study author Couch said that "the military's management and handling of these injuries has changed gradually but dramatically over time. In 2002 they'd probably say, 'Oh, you just got your bell rung a little bit; now get back out there.' Now they say, 'You got your bell rung and you're going to have to take off a day or two and we'll reevaluate and see if we can put you back on the line.'"
Physically, today's soldiers are much better protected, he said. "The helmets are far, far ahead of what was being used in World War II or in the Korean War, Vietnam," Couch noted.
He hopes to continue his research with a 10-year controlled, prospective study.
"We need to pair up the traumatic brain injury person with a person who is race-sex-deployment matched, and try to find out what types of problems arise just from being deployed to a high-danger, high-intensity situation where a person's got to be vigilant and highly alert all the time," Couch said.
Cohen said that the long-term prospects of head-injured soldiers warrant study. "Are these people more likely to die?" he said. "We know that people with severe head trauma are more likely to develop certain types of dementia. Not just eight years down the line, but what happens 30 years down the line?"
The study is scheduled for presentation this week at the American Headache Society's annual meeting in Los Angeles. The data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.
Explore further: Study links PTSD to hidden head injuries suffered in combat
More information: The Defense and Veterans Brain Injury Center has more about combat-related traumatic brain injury.