Brain Health in Older Age Linked to Geographic Location  

July 18, 2017

LONDON — Cognitive function in later life is related to both the geographic area of birth and the neighborhood of current residency, new studies suggest.

The two studies were both presented at here at the Alzheimer's Association International Conference (AAIC) 2017.

In one study, researchers showed that people not currently diagnosed with any dementia or cognitive impairment who were living in neighborhoods in Wisconsin with the highest level of deprivation had much worse cognitive performance in all aspects measured, even after adjustment for age and education. They also had higher levels of the Alzheimer's disease biomarker P-tau.

"We found a very strong effect of living in the most disadvantaged neighborhoods on cognitive health — equivalent to a decline from average to very low average cognitive function," lead author, Amy Kind, MD, PhD, University of Wisconsin School of Medicine and Public Health, Madison, commented to Medscape Medical News.

Dr Amy Kind

"Our results show that where you live does appear to affect brain health — down to individualized neighborhood. We believe the neighborhood is an independent risk factor separate to individualized socioeconomic factors," Dr Kind added. "Other studies have found that when people move to a better area their health improves. even if individual socioeconomic factors do not improve."

She suggested the effect of neighborhood on cognitive heath could be brought about by toxic exposures, safety issues, and the ability to follow a healthy lifestyle.

"In these very deprived areas, it can be difficult to find fresh fruit and vegetables, and it can also be hard to find open spaces to exercise safely, so even if you want to follow healthy lifestyle advice it can be hard to do so. But the good thing about this is that we can identify these neighborhoods and find these people, and we may be able to modify this risk factor," Dr Kind said.

"There is potential for federal or state intervention to try and change this trajectory by targeting additional services and healthcare to these areas to try and reduce the dementia risk in these communities."

In the other study, which was conducted in a cohort of elderly people currently living in northern California, African Americans born in 1 of the 10 US states with the highest infant mortality in 1928 (a surrogate for extreme poverty) had a much higher risk for dementia in older age than those not born in states with high levels of infant mortality. No such relationship was seen in the white population.

"Our study shows that where you were born can affect brain health later in life, even if you no longer live there," study coauthor Rachel Whitmer, PhD, Kaiser Permanente Northern California Division of Research, commented. "What is particularly provocative about our data is that all these people were living in northern California by the time they were in their mid-50s, but just being born in states with high infant mortality rates put them at increased risk of poor cognitive health in older age."

Dr Rachel Whitmer

"We're starting to understand how early life is setting the brain up for the rest of life," she added. "The processes in the brain underlying dementia take a lifetime to evolve. It is too late to start thinking about our cognitive health in later life. The poverty, sanitation, and environmental factors experienced in early life seem to play an important role in brain health throughout life. Our results really speak to social policy programs to target these areas." 

On the observation that the association was seen only in the black population, she said, "It looks as though this risk factor — being born in poverty — has a bigger effect on the black population, as is also seen with many other risk factors for Alzheimer's. But the black population had much higher rates of high infant mortality, so the association may be easier to show in this group."

Moderating an AAIC press conference on the studies, Mary Sano, PhD, Alzheimer's Association Medical and Scientific Advisory Council, said, "These results drive home the risks of social disadvantage on both current and future brain heath and highlight yet again the particular issues regarding higher risks in the black population."

Focus on Neighborhood

For the current geographic neighborhood study, Dr Kind and colleagues applied a metric of neighborhood disadvantage to data from 1479 people enrolled in the Wisconsin study on Alzheimer's disease (WRAP) — a long-term study that tracked people without cognitive impairment at baseline but with a parental history of Alzheimer's disease and compared them with a control group.  Participants undergo regular cognitive testing and cerebrospinal fluid (CSF) measures of Alzheimer's biomarkers.

After adjustment for age and education, results showed strong reductions of cognitive function in participants living in the lowest socioeconomic decile compared with those in the other nine deciles.

Table. Baseline Cognitive Outcomes for Most Disadvantaged Neighborhood Decile vs All Others

Cognitive Area β-Coefficient (95% Confidence Interval)
Working memory –0.45 (–0.62 to –0.28)
Immediate memory –0.34 (–0.52 to –0.17)
Speed and flexibility –0.62 (–0.78 to –0.45)
Verbal learning and memory –0.44 (–0.61 to –0.27)
P value for all cognitive areas was <.0001.

 

Dr Kind said the β-coefficient values were "much higher" than those seen in studies of other risk factors, suggesting that living in a disadvantaged neighborhood was a particularly strong risk factor for lower cognitive function.

The study also found that people living in the lowest decile neighborhoods had higher P-tau levels (by 11.61 units) than the other areas together. This didn't quite reach significance (P = .064). There was no difference in amyloid levels. 

"Tau is a marker of neurodegeneration, so this raises a whole host of questions as to what is going on in the brains of these subjects," Dr Kind commented. "But these results came from a very limited sample size — with CSF samples only available in 153 people — so we have to be cautious on their interpretation."

Risk Starts at Birth

For the place of birth study, researchers evaluated data on 6284 elderly individuals currently living in northern California and members of the Kaiser Permanente health plan (17% black, 83% white) who were born between 1919 and 1932 and had health survey and clinical exam data collected between 1964 and 1973. Dementia diagnoses were found by International Classification of Diseases codes.

The researchers looked specifically at place of birth and focused on individuals born in 1 of the 10 states with the highest rate of race-specific infant mortality in 1928.

Rates of infant mortality were much higher among blacks (median, 116 deaths/1000 live births) than whites (median, 64 deaths/1000 live births). 

After adjustment for age and sex, birth in one of the states with the highest infant mortality was not associated with higher risk for dementia among white participants (hazard ratio [HR], 1.01).

However, black participants born in the states with highest infant mortality had 40% elevated risk (HR, 1.40; 95% confidence interval,  1.02 - 1.91), which persisted after adjustment for education and comorbidities throughout the life course even though all individuals subsequently moved to California.

Dr Whitmer noted that African Americans not born in the states with the highest infant mortality had a 40% increased risk for dementia compared with whites also not born in these states. But African Americans born in 1 of the 10 poorest states had an 86% increased risk for dementia compared with whites not born in these poorest states.

Both studies were funded by grants from the National Institutes of Health. Dr Kind and Dr Whitmer have disclosed no relevant financial relationships.

Alzheimer's Association International Conference (AAIC) 2017. Abstracts 14725 and 19320. Presented July 16, 2017.

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