Birthplace linked to dementia risk

A person’s place of birth influences their risk for dementia and also may also be a significant contributor to racial disparities according to research recently published in JAMA Neurology.

Birth in the Stroke Belt, a cluster of states in the South where people are known to have an increased risk for several conditions, is linked to a greater risk for dementia mortality, according to researchers. This association persisted regardless of residence at death.

“To our knowledge, no prior study has examined whether incident dementia is similarly elevated for individuals born in geographic regions with high stroke risk but who subsequently reside elsewhere,” Paola Gilsanz, ScD of the division of research at Kaiser Permanente and colleagues wrote.

Researchers conducted an observational cohort study of 7,423 people who once lived in

Alabama, Alaska, Arkansas, Louisiana, Mississippi, Oklahoma, Tennessee, South Carolina and West Virginia, all of which are known as high stroke mortality states (HSMS). Of the participants, 54.5% were women and 18.2% were black.

The participants’ birthplace, level of education, race, and midlife heart disease-related risk factors were collected between 1964 and 1973. Electronic health records from Jan. 1, 1996, through Oct. 15, 2015, provided dementia diagnoses. The mean age of the participants was 42.94 years at their first visit. At the start of the follow-up period, all participants had moved to California and their mean age was 71.14 years.

Gilsanz and colleagues found that dementia was diagnosed in 30.4% of the participants and was more likely to occur (39%) among those born in an HSMS than those born outside of

one (28.8%). Being born in an HSMS was linked to a 28% higher risk for dementia (adjusted HR = 1.28; 95% CI, 1.13-1.46) when data were adjusted for age, sex and race.

Black participants were 9.6 times more likely to have been born in an HSMS. Researchers also found that black individuals born in an HSMS had the highest dementia risk (adjusted HR = 1.67; 95% CI, 1.48-1.88), followed by black individuals not born in an HSMS (aHR = 1.48; 95% CI, 1.28-1.72). Nonblack individuals born in an HSMS had a 46% increased risk (aHR, 1.46; 95% CI, 1.23-1.74). Overall, the 20-year dementia risks at age 65 years were 30.13% (95% CI, 26.87-32.93) for those born within an HSMS and 21.8% (95% CI, 20.51-22.91) for those born outside of one.

“To our knowledge, this is the first study of place of birth and risk of incident dementia,”

Gilsanz and colleagues wrote. “Future research should examine possible pathways through

which early-life biological and psychosocial exposures affect dementia risk, [and] address

the geographic patterning of dementia and elucidate the effect of place over the life course on health.”

The researchers also suggested that such analyses be performed among different population groups to get as broad a sample as possible.

In a related editorial, Daniel T. Lackland, DrPH, of the department of neurology at the Medical University of South Carolina, wrote that the study can help others comprehend the role geography can play in certain medical conditions, but that future work on its function must be done.

“The current study contributes a better understanding of the factors associated with the geographic disparity in cerebrovascular disease, which is a critical area of need given the

high burden. Although the effect of elevated blood pressure on cerebrovascular disease risk has been clearly documented, as well as the benefit from blood pressure reduction, the influence of geography remains at or near the same levels as in previous decades,” Lackland wrote. “With the assessment of the geographic risks associated with dementia, Gilsanz et al have restated the need for continued assessment of the excess disease burden in high-risk populations.”– by Janel Miller

Disclosure: The researchers report no relevant financial disclosures.