Risk of Dementia Later in Life Linked to Stroke Mortality Rate At Birth

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Non-black individuals born in an HSMS had a 46% increase in dementia risk.
Non-black individuals born in an HSMS had a 46% increase in dementia risk.

Birth in a high stroke mortality state (HSMS) significantly increases risk for dementia later in life, especially in black individuals, according to a study published in JAMA Neurology.

Paola Gilsanz, ScD, of the University of California, San Francisco, and colleagues conducted an observational cohort study in 7423 participants to determine whether birth in an HSMS is linked to an increased risk of dementia. The 9 HSMSs evaluated in the study were Alabama, Alaska, Arkansas, Louisiana, Mississippi, Oklahoma, Tennessee, South Carolina, and West Virginia.

Health data were gathered from the Kaiser Permanente Northern California health system from 1964 to 1973, when participants were age 40 to 45, and 1996 to 2015, when participants were in later life. Overall, the sample was 74.2% white, 18.2% black, and 5.0% Asian; 15.7% were born in an HSMS, and of those, 68.2% were black.

By the end of the study, 2254 (30.4%) of the participants were diagnosed with dementia. Birth in an HSMS was associated with a 54% increased risk of dementia (adjusted hazard ratio [aHR] 1.54; 95% Cl, 1.39-1.71), which remained significant after adjusting for black race (aHR 1.28; 95% Cl, 1.13-1.46), compared with birth outside of those states. After adjusting for age and sex, non-black individuals born in an HSMS had a 46% increase in dementia risk, while black individuals born in an HSMS had a 13% increased risk of dementia (aHR 1.13; 95% Cl, 0.94-1.35).

In models analyzing the joint effects of being born in an HSMS and race, with adjustment for sex and age, black individuals born in an HSMS had the greatest risk of dementia (aHR 1.67; 95% Cl, 1.48-1.88), followed by black individuals born outside of an HSMS (aHR 1.48; 95% Cl, 1.28-1.72) and nonblack individuals born in an HSMS (aHR 1.46; 95% Cl, 1.23-1.74).

Birthplace remained a significant risk factor for dementia, even after adjusting for educational levels, race, and life-course vascular risk factors, and this was especially true in black individuals.

“This has great public health relevance since many current black elderly individuals were born in the South and moved away during the ‘great migration,'” the researchers wrote.

“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,” Daniel T. Lackland, DrPH, professor in the department of neurology at the Medical University of South Carolina in Charleston, commented on the study.2 “Dr Gilsanz, et al, restated the need for continued assessment of the excess disease burden in high-risk populations.”

The researchers made note of the following limitations as they may have affected the study's outcomes:

  • because all participants migrated to California, a possible selection bias may have been introduced, leading to the study to  underestimate the effect of birth in a HSMS
  • researchers did not have access to complete residential history and could not determine how long participants had resided in an HSMS; therefore, the study could not determine whether longer time of residence affected the risk of dementia
  • researchers did not have information on the childhood exposure of participants to risk factors
  • researchers did not have brain imaging data in the sample and therefore were unable to analyze subclinical vascular brain injury

References

  1. Gilsanz P, Mayeda ER, Glymour MM, Quesenberry CP, Whitmer RA. Association between birth in a high stroke mortality state, race, and risk of dementia [published online July 31, 2017]. JAMA Neurol. doi:10.1001/jamaneurol.2017.1553
  2. Lackland DT. Impact of birthplace and geographic location on risk disparities in cerebrovascular disease: implications for future research [published online July 31, 2017]. JAMA Neurol. doi:10.1001/jamaneurol.2017.1560
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