Researchers found that traumatic brain injury sustained at the age of 55 or over may increase the risk of dementia.
This is not the first study to suggest such a link. Earlier this year, Medical News Today reported on a study revealing that 16% of veterans who had experienced a traumatic brain injury (TBI) developed dementia, compared with only 10% of veterans who had not experienced a TBI.
However, the researchers of this latest study - including Dr. Raquel C. Gardner of the University of California-San Francisco - note that other studies have not found a link between TBI and dementia, but such studies have been subject to many limitations.
"Even among studies that report a positive association between TBI and dementia, marked variability exists in the magnitude of reported risk," the researchers add, "which may be due to differences in TBI severity, age of patients, and follow-up period - with some being as short as 2 years - among studies."
According to the Centers for Disease Control and Prevention (CDC), 60% of all hospitalizations for TBI occur among individuals aged 55 and older. The highest rates of TBI-related emergency department (ED) visits, inpatient stays and deaths occur among individuals aged 75 years and older.
Dr. Gardner and colleagues say such figures emphasize the need to gain a better understanding of the relationship between TBI and dementia - something they set out to do with this latest study.
Moderate, severe TBI at age 55 or older linked to increased dementia risk
Using information from a health database of ED and inpatient visits in California, the research team identified 164,661 patients aged 55 years and older who were recently diagnosed with TBI or non-TBI body trauma (NTT) - fractures that occurred in areas of the body other than the head or neck.
The researchers note that few studies assessing the link between TBI and dementia have used patients with NTT as controls. Doing so strengthens the study results, they say, as it mitigates the possibility of reverse causality.
Patients were followed-up for an average of 5.7 years and had no signs of dementia at study baseline.
Of the 51,799 patients diagnosed with TBI, 8.4% developed dementia, compared with 5.9% of patients diagnosed with NTT. TBI patients also had a shorter duration between trauma and development of dementia, at 3.1 years compared with 3.3 years among NTT patients.
Further analysis revealed that moderate to severe TBI at age 55 years or older was associated with increased risk of dementia, as was mild TBI at age 65 years or older.
Commenting on their findings, the team says:
"Given the high rates of TBI in the population, primary prevention of TBI, which in this study was overwhelmingly (66.4%) due to falls, is critical.
The effect of mild TBI sustained in middle age or earlier deserves further study during a longer period of follow-up. In addition, further research is needed to understand the mechanisms of post-TBI dementia to inform secondary preventive strategies."
They add that there are some limitations to their study. For example, they used information from ED and inpatient databases, in which patients could have been subject to misdiagnoses or miscoding.
Furthermore, they lacked data on patients' family history, educational status and previous TBIs, illnesses or operations, which could have influenced the results.
In an editorial linked to the study, Dr. Steven T. DeKosky, of the University of Pittsburgh School of Medicine, PA, notes that although the researchers cited having NTT patients as controls a study strength, it is also a limitation.
"Unfortunately, there was not a non-trauma control group included, which may have answered the question of whether NTT (i.e. body trauma itself) raised the risk of dementia significantly above age-equivalent controls without non-brain trauma (perhaps from inflammation or other complications)," he says, adding:
"If the non-brain trauma population had incident rates similar to non-traumatized age-equivalent controls, trauma could be ruled out as a risk factor and more specific effects of brain injury can be examined for their contribution to eventual dementia."
MNT recently reported on a study revealing that a walnut-enriched diet slowed progression of Alzheimer's - the most common form of dementia - in mice.