WEDNESDAY, Sept. 19, 2018 (HealthDay News) -- Brain injury research typically focuses on football players and military veterans, but a new study suggests head injuries are far more widespread than estimated.
About 1 in every 6 U.S. adults -- roughly 23 million people aged 40 or older -- have been knocked out by a head injury, researchers report.
"Those numbers are huge," said lead researcher Dr. Andrea Schneider, a neurologist with Johns Hopkins University in Baltimore. "Head injury in the United States is much more common than we thought."
Further, these head injuries are associated with neurological and psychological problems such as depression, sleep disorders, stroke and alcoholism, the researchers found.
For this study, Schneider and her colleagues relied on data gathered by the National Health and Nutrition Examination Survey, which is conducted by the U.S. Centers for Disease Control and Prevention.
The data showed that nearly 16 percent of U.S. adults aged 40 and older answered yes to the question, "Have you ever had loss of consciousness because of a head injury?"
Men were nearly twice as likely to have answered yes, about 20 percent compared with 12 percent among women.
This could be because men are more involved in careers and pastimes with an increased risk of head injury, such as military service or contact sports, Schneider said.
People who reported a head injury that knocked them out were 54 percent more likely to have a sleep disorder, 68 percent more likely to have had a stroke, twice as likely to be a heavy drinker, and more than twice as likely to have symptoms of depression.
However, researchers can't say from this data which way the relationship runs between head injury and these health problems, Schneider said.
It could be that depression or sleeplessness or heavy drinking make you more likely to suffer a head injury. It also could be that a head injury increases your risk to subsequently suffer from these problems.
"More prospective studies are needed to look into the directionality of these relationships," Schneider said.
Kristen Dams-O'Connor, co-director of the Brain Injury Research Center of Mount Sinai in New York City, suspects the relationship runs both ways. Head injuries are prompted by these neurological and psychological problems, but the injuries also can either cause new problems or make existing problems worse.
"We may be talking about people who are associated with previous risk factors, and you've now got a traumatic brain injury overlaid upon whatever they were suffering before," said Dams-O'Connor, who wasn't involved with the study.
She believes the number of people who've suffered a brain injury is even higher than found here.
"I think the numbers are impressive. The numbers are staggering. They certainly support the notion that we need to learn a heck of a lot more about how to prevent this injury," Dams-O'Connor said. "But at the end of the day, I think this is definitely an undercount."
The single question used in this survey does not capture all of the potential scenarios in which a traumatic brain injury could occur, Dams-O'Connor explained.
For example, the survey question would not reflect people who were dazed or confused by a blow to the head that did not cause them to lose consciousness, she said.
"That would meet the criteria for a mild traumatic brain injury, and none of those people are even included in this estimate," Dams-O'Connor noted.
It's unknown whether these 23 million or more people are at increased risk for neurological problems like dementia or Parkinson's disease down the road, Dams-O'Connor added.
It's widely suspected that one traumatic brain injury (TBI) doesn't result in the kind of long-term damage caused by repeated brain injuries, she said.
"A substantial number of people sustain a TBI that heals and they return to their normal," Dams-O'Connor said. "These are the lucky ones who go back to their baseline and they don't have long-term symptoms that don't go away. Overall, most people who survive a brain injury are not going to develop these terrible outcomes."
The findings appear in a letter published Sept. 19 in the New England Journal of Medicine.
There's more from the U.S. National Institutes of Health about traumatic brain injury.