Veterans who suffered a moderate or severe concussion during World War II face a heightened risk of Alzheimer’s disease now that they have reached old age, a new study finds. The research reinforces other evidence that brain trauma can set off a long degenerative process resulting in the confusion, memory loss, and disorientation that mark Alzheimer’s disease.
Using Navy and Marine Corps medical documents, researchers identified 548 men who had had a concussion in 1944 or 1945. As a comparison group, the researchers also located 1,228 men who had been treated for lacerations or pneumonia during the war but not head injury. In 1996 and 1997, interviewers telephoned each man to update his medical status, then called a family member to double-check the information.
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While 3.2 percent of the veterans who had had a concussion developed Alzheimer’s disease later, only 1.5 percent of the others did, the researchers report in the Oct. 24 Neurology.
The scientists classified the men as having a mild, moderate, or severe concussion if they were unconscious or had amnesia for less than 30 minutes, 30 minutes to 24 hours, or more than 24 hours, respectively. The data show no more Alzheimer’s among men who had had a mild concussion than among the control group. But men with a moderate concussion were twice as likely to develop Alzheimer’s, and those with a severe concussion showed four times the risk that the control group did.
Past research on boxers and others also found an association between head trauma and Alzheimer’s disease. Unlike some of that work, this study doesn’t rely on a person’s recall to establish a history of head injury, says study coauthor Richard J. Havlik, an epidemiologist at the National Institute on Aging in Bethesda, Md. Because of the nature of Alzheimer’s, he says, documentation of medical histories is crucial. Indeed, in this study, nearly a third of the men who had been hospitalized for a concussion during military service didn’t recall the incident.
The cause of Alzheimer’s disease remains unknown, although genetic variations seem to play a role in some people (SN: 7/25/98, p. 55). This study offers “one more good example of the nongenetic association between brain trauma and Alzheimer’s disease,” says neuroscientist Douglas H. Smith of the University of Pennsylvania in Philadelphia. “Brain trauma may be the strongest environmental cause [of Alzheimer’s disease] out there.”