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Original Investigation
September 2017

Association Between Birth in a High Stroke Mortality State, Race, and Risk of Dementia

Author Affiliations
  • 1Division of Research, Kaiser Permanente, Oakland, California
  • 2Department of Epidemiology and Biostatistics, University of California, San Francisco
  • 3Department of Epidemiology, Fielding School of Public Health, University of California, Los Angeles
JAMA Neurol. 2017;74(9):1056-1062. doi:10.1001/jamaneurol.2017.1553
Key Points

Question  Is birth in a state with high stroke mortality associated with dementia risk in a cohort of individuals who all subsequently resided outside of those states?

Findings  In this cohort study, among 7423 Northern California residents with equal access to health care, dementia risk was approximately 27% higher among those born in high stroke mortality states compared with elsewhere. Compared with nonblack persons born outside of high stroke mortality states, black individuals born in a high stroke mortality state had the highest dementia risk, followed by black individuals not born in a high stroke mortality state, and lastly nonblack persons born in a high stroke mortality state.

Meaning  Racial inequalities in dementia may partially reflect geographic patterning of early-life exposures.

Abstract

Importance  Birth in a group of predominantly southern US states is robustly linked to increased stroke risk. Given the role of cerebrovascular disease in dementia risk, geographic patterning may also occur for dementia incidence.

Objective  To determine whether birth in 9 high stroke mortality states (HSMSs) is associated with dementia in a diverse cohort of individuals living in Northern California.

Design, Setting, and Participants  An observational cohort study included 7423 members of Kaiser Permanente Northern California (KPNC), an integrated health care delivery system, with health survey and clinical examination data available. Data were collected between 1964 and 1973 when the individuals were middle-aged and 1996 and 2015 when participants were in later life.

Exposures  Self-reported state of birth in an HSMS (top quintile of states for stroke mortality).

Main Outcomes and Measures  Dementia diagnoses obtained from electronic health records from January 1, 1996, to October 15, 2015. Place of birth, race, educational level, and midlife vascular risk factors data were collected between 1964 and 1973.

Results  Of the 7423 persons included in the analysis, 4049 (54.5%) were women; 1354 (18.2%) were black. The mean (SD) age of study participants at their first visit between 1963 and 1974 was 42.94 (1.73) years and mean (SD) age at the beginning of follow-up for dementia in 1996 was 71.14 (2.72) years. Dementia was diagnosed in 2254 (30.4%) of the participants and was more common among those born in an HSMS than those born outside of one (455 [39.0%] vs 1799 [28.8%]). Birth in an HSMS was 9.6 times more common for black participants (795 [58.7%]) than nonblack participants (371 [6.1%]). Overall, birth in an HSMS was associated with a 28% higher risk of dementia (adjusted hazard ratio [aHR], 1.28; 95% CI, 1.13-1.46) adjusted for age, sex, and race. Compared with nonblack persons born outside of an HSMS, black individuals born in an HSMS had the highest dementia risk (aHR, 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), and nonblack persons born in an HSMS had a 46% increased risk (aHR, 1.46; 95% CI, 1.23-1.74). Cumulative 20-year dementia risks at age 65 years were 30.13% (95% CI, 26.87%-32.93%) and 21.80% (95% CI, 20.51%-22.91%) for individuals born in and outside an HSMS, respectively.

Conclusions and Relevance  To our knowledge, this is the first study to date of place of birth and incident dementia and shows increased risk for individuals born in an HSMS, even though all participants subsequently resided in California. Birth in an HSMS was common among black participants. Place of birth has enduring consequences for dementia risk and may be a major contributor to racial disparities in dementia.

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