Interactive Effect of Traumatic Brain Injury and Psychiatric Symptoms on Cognition among Late Middle-Aged Men: Findings from the Vietnam Era Twin Study of Aging.

Traumatic brain injury (TBI), post-traumatic stress disorder (PTSD), and depressive symptoms each increase the risk for cognitive impairment in older adults. We investigated whether TBI has long-term associations with cognition in late middle-aged men, and examined the role of current PTSD/depressive symptoms. Participants were 953 men (ages 56-66) from the Vietnam Era Twin Study of Aging (VETSA), who were classified by presence or absence of (1) history of TBI and (2) current elevated psychiatric symptoms (defined as PTSD or depressive symptoms above cutoffs). TBIs had occurred an average of 35 years prior to assessment. Participants completed cognitive testing examining nine domains. In mixed-effects models, we tested the effect of TBI on cognition including for interactions between TBI and elevated psychiatric symptoms. Models adjusted for age, pre-morbid cognitive ability assessed at average age 20 years, apolipoprotein E genotype, and substance abuse; 33% (n = 310) of participants had TBI, mostly mild and remote; and 23% (n = 72) of those with TBI and 18% (n = 117) without TBI had current elevated psychiatric symptoms. TBI and psychiatric symptoms had interactive effects on cognition, particularly executive functioning. Group comparison analyses showed that men with both TBI and psychiatric symptoms demonstrated deficits primarily in executive functioning. Cognition was largely unaffected in men with either risk factor in isolation. Among late middle-aged men, the combination of even mild and very remote TBI with current elevated psychiatric symptoms is associated with deficits in executive function and related abilities. Future longitudinal studies should investigate how TBI and psychiatric factors interact to impact brain aging.