Previous studies indicate that head injury is associated with substantial morbidity and mortality, as well as short-term cognitive impairment.  New research also suggests that a history of head injury carries a greater risk for dementia over the following 20 years when compared with no such history. However, the extent of the long-term associations with cognitive change in the general U.S. population has not been well characterized.

Assessing the Link

For a study published in the New England Journal of Medicine, Andrea L.C. Schneider, MD, PhD, and colleagues examined a nationally representative sample in the U.S. from the 2011–2014 National Health and Nutrition Examination Survey (NHANES) cohort to estimate the prevalence of head injury and its associated risk factors. The research team also assessed data from participants in the ongoing Atherosclerosis Risk in Communities (ARIC) trial.

A total of 13,192 participants were followed from baseline (1990-1992) to January 1, 2013. Participants underwent three cognitive assessments (1990-1992, 1996-1998, and 2011-2013) comprised of three tests that were combined into a global cognitive Z-score. During a median follow-up of 20 years, 24% of participants experienced at least one head injury, ranging from mild concussion with or without loss of consciousness to moderate/severe traumatic brain injury.

Important Findings

After adjusting for factors such as age, sex, race, hypertension, and stroke in the ARIC study, Dr. Schneider and colleagues observed that decreases in cognitive decline were observed in both the participants who had had head injuries and those who had not. Those sustaining at least one or more head injuries showed significantly greater cognitive decline than those who had not had a head injury.

“In the NHANES study, we found that nearly 16% of U.S. adults aged 40 years or older have suffered a head injury with concussion (Table),” says Dr. Schneider. “That represents 23 million adults. We also determined that people who have had a head injury are much more likely to have sleep disorders, alcohol disorders, stroke, and other conditions affecting their brains.” Estimates from the study suggest a higher risk among men (20.0%) than women (12%) and among non-Hispanic white respondents (18.0%) than non-Hispanic black respondents (8.9%). Risk factors associated with head injury included smoking, fair to poor health, sleep disorders, heavy alcohol consumption, a history of stroke, and depressive symptoms. Head injury was most common among respondents with a college education (17.3%) but also occurred at high frequency among those with lower family income (16.4%).

Based on neuropsychologic tests, telephone interviews, and hospitalization/death certificate codes, 1,295 cases of incident dementia occurred among ARIC study participants. These cases included 895 patients without head injury and 400 patients with a history of head injury. The median time from head injury to dementia in the head injury group was 17 years. Participants who experienced a head injury showed a 1.5 times increased risk for incident dementia after a multivariate adjustment for key risk factors.

Making Head Injury a Priority

Dr. Schneider notes that the increased cognitive decline for participants with a history of head injury was equivalent to that of a person without head injury who was approximately 4 years older at study baseline. “Taking into consideration the results of this study along with the results of the ARIC study on head injury and dementia risk, head injury is a major unrecognized problem in the U.S. population that can have serious consequences,” she says. “While our results suggest that head injury should be a public health priority, more research is needed prior to recommending any changes in clinical practice. And although contributions of both tau and beta-amyloid have been hypothesized to play a role, studies are need to shed light on the mechanism(s) whereby head injury may lead to cognitive impairment and dementia.