Living in highly disadvantaged areas increases brain degeneration, cognitive decline

Living in the most disadvantaged neighborhoodss correlated with increased degeneration in Alzheimer’s disease “signature” regions of the brain and cognitive decline, according to the results of a longitudinal study in cognitively healthy adults.

The results of the study, which were published in Neurology, provided additional evidence “for neighborhood-level disadvantage as a risk factor for preclinical neurodegeneration and cognitive decline” among certain groups, according to the researchers.

“Worldwide, dementia is a major cause of illness and a devastating diagnosis. There are currently no treatments to cure the disease, so identifying possible modifiable risk factors is important,” Amy JH Kind, MD, PhD, associate professor and member of the geriatrics faculty in the department of medicine at the University of Wisconsin School of Medicine and Public Health, said in a press release. “Compelling evidence exists that the social, economic, cultural and physical conditions in which humans live may affect health. We wanted to determine if these neighborhood conditions increase the risk for the neurodegeneration and cognitive decline associated with the earliest stages of Alzheimer’s disease and dementia.”

Kind and colleagues obtained longitudinal MRI and cognitive testing data from 601 cognitively unimpaired individuals in the Wisconsin Registry for Alzheimer’s Prevention study and the Wisconsin Alzheimer’s Disease Research Center clinical cohort. The researchers determined the Area Deprivation Index geospatially according to the individual’s residence geocode and ranked it in relation to the state of residence. They used linear regression models to examine relationships between neighborhood-level disadvantage and longitudinal change in cortical thickness and performance on cognitive tests. They also used mediation tests to determine whether neurodegeneration and cognitive decline were related to neighborhood-level disadvantage “along the same theoretical causal path,” according to the study results.

The study included 582 participants (96.8%) in the 80% least disadvantaged neighborhoods relative to the state of residence and 19 (3.2%) in the 20% most disadvantaged neighborhoods. Compared with the 20% most neighborhood-level disadvantaged group, the 80% least disadvantaged group included significantly fewer Black and more white participants and a significantly longer time between baseline and follow-up MRI scans, “likely due to participants having underwent one additional study related MRI scan,” according to the results from Kind and colleagues.

In the middle-to-older age group (mean baseline age, 59 years), living in the 20% most disadvantaged neighborhoods in relation to the state of residence correlated with cortical thinning in Alzheimer’s disease “signature” regions of the brain (P = .002) as well as decline in the Preclinical Alzheimer’s disease Cognitive Composite (P = .04), particularly the Trails-Making Test Part B (P < .001), but not the Rey Auditory Verbal Learning Test or the Story Memory Delayed Recall subtests. The researchers found that associations were lessened, but remained significant, after controlling for racial and demographic differences between the neighborhood-level disadvantage groups. The study results also showed that cortical thinning partially mediated the relationship between neighborhood-level disadvantage and cognitive decline.

“Accelerated decline in TMT-B, a test of executive function and processing speed, was particularly prominent and was statistically mediated by cortical thinning in AD signature regions,” the researchers wrote.

Study limitations included the small number of individuals from highly disadvantaged neighborhoods and a limited geographic setting, according to the press release. Kind and colleagues noted that future studies should assess larger, more diverse groups over longer periods.

“Our findings suggest that increased vigilance by health care providers for early signs of dementia may be particularly important in this vulnerable population,” Kind said in the press release. “Some possible causes of these brain changes may include air pollution, lack of access to healthy food and health care and stressful life events. Further research into possible social and biological pathways may help physicians, researchers and policymakers identify effective avenues for prevention and intervention in Alzheimer’s disease and related dementia.”