An analysis of more than 13,000 adult participants in the Atherosclerosis Risk in Communities (ARIC) study showed a dose-response pattern in which one head injury was linked to a 66% increased risk for all-cause mortality, and two or more head injuries were associated with twice the risk in comparison with no head injuries.
These findings underscore the importance of preventing head injuries and of swift clinical intervention once a head injury occurs, lead author Holly Elser, MD, PhD, department of neurology, Hospital of the University of Pennsylvania, Philadelphia, told this news organization.
“Clinicians should counsel patients who are at risk for falls about head injuries and ensure patients are promptly evaluated in the hospital setting if they do have a fall – especially with loss of consciousness or other symptoms, such as headache or dizziness,” Dr. Elser added.
The findings were published online in JAMA Neurology.
Consistent evidence
There is “pretty consistent evidence” that mortality rates are increased in the short term after head injury, predominantly among hospitalized patients, Dr. Elser noted.
“But there’s less evidence about the long-term mortality implications of head injuries and less evidence from adults living in the community,” she added.
The analysis included 13,037 participants in the ARIC study, an ongoing study involving adults aged 45-65 years who were recruited from four geographically and racially diverse U.S. communities. The mean age at baseline (1987-1989) was 54 years; 57.7% were women; and 27.9% were Black.
Study participants are followed at routine in-person visits and semiannually via telephone.
Data on head injuries came from hospital diagnostic codes and self-reports. These reports included information on the number of injuries and whether the injury required medical care and involved loss of consciousness.
During the 27-year follow-up, 18.4% of the study sample had at least one head injury. Injuries occurred more frequently among women, which may reflect the predominance of women in the study population, said Dr. Elser.
Overall, about 56% of participants died during the study period. The estimated median amount of survival time after head injury was 4.7 years.
The most common causes of death were neoplasm, cardiovascular disease, and neurologic disorders. Regarding specific neurologic causes of death, the researchers found that 62.2% of deaths were due to neurodegenerative disease among individuals with head injury, vs. 51.4% among those without head injury.
This, said Dr. Elser, raises the possibility of reverse causality. “If you have a neurodegenerative disorder like Alzheimer’s disease dementia or Parkinson’s disease that leads to difficulty walking, you may be more likely to fall and have a head injury. The head injury in turn may lead to increased mortality,” she noted.
However, she stressed that the data on cause-specific mortality are exploratory. “Our research motivates future studies that really examine this time-dependent relationship between neurodegenerative disease and head injuries,” Dr. Elser said.
Dose-dependent response
In the unadjusted analysis, the hazard ratio of mortality among individuals with head injury was 2.21 (95% confidence interval, 2.09-2.34) compared with those who did not have head injury.
The association remained significant with adjustment for sociodemographic factors (HR, 1.99; 95% CI, 1.88-2.11) and with additional adjustment for vascular risk factors (HR, 1.92; 95% CI, 1.81-2.03).
The findings also showed a dose-response pattern in the association of head injuries with mortality. Compared with participants who did not have head injury, the HR was 1.66 (95% CI, 1.56-1.77) for those with one head injury and 2.11 (95% CI, 1.89-2.37) for those with two or more head injuries.
“It’s not as though once you’ve had one head injury, you’ve accrued all the damage you possibly can. We see pretty clearly here that recurrent head injury further increased the rate of deaths from all causes,” said Dr. Elser.
Injury severity was determined from hospital diagnostic codes using established algorithms. Results showed that mortality rates were increased with even mild head injury.
Interestingly, the association between head injury and all-cause mortality was weaker among those whose injuries were self-reported. One possibility is that these injuries were less severe, Dr. Elser noted.
“If you have head injury that’s mild enough that you don’t need to go to the hospital, it’s probably going to confer less long-term health risks than one that’s severe enough that you needed to be examined in an acute care setting,” she said.
Results were similar by race and for sex. “Even though there were more women with head injuries, the rate of mortality associated with head injury doesn’t differ from the rate among men,” Dr. Elser reported.
However, the association was stronger among those younger than 54 years at baseline (HR, 2.26) compared with older individuals (HR, 2.0) in the model that adjusted for demographics and lifestyle factors.
This may be explained by the reference group (those without a head injury) – the mortality rate was in general higher for the older participants, said Dr. Elser. It could also be that younger adults are more likely to have severe head injuries from, for example, motor vehicle accidents or violence, she added.
These new findings underscore the importance of public health measures, such as seatbelt laws, to reduce head injuries, the investigators note.
They add that clinicians with patients at risk for head injuries may recommend steps to lessen the risk of falls, such as having access to durable medical equipment, and ensuring driver safety.
Shorter life span
Commenting for this news organization, Frank Conidi, MD, director of the Florida Center for Headache and Sports Neurology in Port St. Lucie and past president of the Florida Society of Neurology, said the large number of participants “adds validity” to the finding that individuals with head injury are likely to have a shorter life span than those who do not suffer head trauma – and that this “was not purely by chance or from other causes.”
However, patients may not have accurately reported head injuries, in which case the rate of injury in the self-report subgroup would not reflect the actual incidence, noted Dr. Conidi, who was not involved with the research.
“In my practice, most patients have little knowledge as to the signs and symptoms of concussion and traumatic brain injury. Most think there needs to be some form of loss of consciousness to have a head injury, which is of course not true,” he said.
Dr. Conidi added that the finding of a higher incidence of death from neurodegenerative disorders supports the generally accepted consensus view that about 30% of patients with traumatic brain injury experience progression of symptoms and are at risk for early dementia.
The ARIC study is supported by the National Heart, Lung, and Blood Institute. Dr. Elser and Dr. Conidi have reported no relevant financial relationships.
A version of this article originally appeared on Medscape.com.