A recent JAMA Network Open study investigates whether socioeconomic status transitions throughout an individual’s lifespan impact their risk of dementia.
Study: Socioeconomic Status Transition Throughout Life and Risk of Dementia. Image Credit: Toa55 / Shutterstock.com
Dementia risk and socioeconomic status
Dementia, which is an umbrella term used to describe the severely impaired ability to remember, think, or make decisions, comprises various conditions, the most common of which include Alzheimer’s disease (AD). Several factors have been shown to increase the risk of dementia, some of which include smoking, exposure to air pollution, alcohol use, and low socioeconomic status (SES).
Previous studies have identified several SES components, such as limited education, lower childhood SES, and lower household income in adulthood, that increase the risk of dementia onset. Thus, it is crucial to understand the association between social mobility and healthy longevity. To date, few studies have evaluated the effect of changing SES throughout an individual’s life on the risk of dementia.
About the study
The current study used data from the Japan Gerontological Evaluation Study (JAGES) cohort to determine the association of SES classification with dementia incidence and dementia-free periods during an individual’s lifetime.
Individuals from 31 Japanese regions were recruited to the JAGES cohort between August 2010 and December 2016. All study participants were 65 or older, not diagnosed with dementia, and not registered for long-term care or health and welfare social services.
At baseline, life-course SES components were self-reported. To this end, all study participants were asked about their childhood SES, and their responses were assessed on a three-point Likert scale. In this scale, one represented very low/low SES, two indicated middle SES, and three represented a high/very-high SES.
Study participants’ years of formal education, the longest-held job in middle age, and pre-tax household income were assessed. To determine potential dementia risk factors, participants’ demographic variables, comorbidities, physical characteristics, social factors, and lifestyle behaviors were reported at baseline.
Dementia was diagnosed following a standardized protocol. The cognitive functions of the participants were also measured.
Study findings
Participants with an upward SES trend had the lowest dementia risk and the greatest gain of dementia-free periods. In contrast, participants with downward SES transitions experienced the largest reduction in healthy lifespan periods at an older age.
A total of 55,067 participants were recruited in the JAGES cohort, 12,398 of whom were randomly selected for life-course SES assessment. Participants with missing SES values, loss of follow-up, and new dementia onset one year or less from baseline were removed, leading to a final study cohort of 9,186 individuals.
The mean age of the participants at baseline was 74.2 years, 51% of whom were men and 49% women. A total of 800 cases of dementia were estimated within 6.4 years of follow-up. Among 9,186 individuals, 7.5% died without a dementia diagnosis, and 2.9% died with dementia.
Individuals with upward SES transitions were associated with the lowest dementia incidence. Therefore, upward SES patterns during life aided in dementia prevention. This observation suggests that successful experiences throughout an individual’s life may decelerate cognitive aging by enhancing stress resistance.
Individuals with upward SES transition exhibited the lowest prevalence of mental health disorders and the highest sense of coherence. Physical characteristics, comorbidities, lifestyle behaviors, and social factors varied among the SES transitions.
Lifestyle behaviors and physical characteristics were key mediators in upward, stable-high, and stable-low SES transitions. However, social factors only influenced downward SES transitions. The SES transitions were robustly associated with higher dementia risks among men and urban residents as compared to women and rural residents.
Strengths and limitations
The main strengths of the current study are the higher response rate at primary screening, the use of standardized dementia detection, and the analysis of SES transition and dementia based on a sizeable multiregional cohort.
Conversely, some notable limitations of the current study include the use of self-reported data, lack of dementia subtype data, and short follow-up periods. Furthermore, there remains a risk of misclassification and unmeasured bias that could influence the study findings.
Despite these limitations, the current study observed a distinct association between SES transition patterns and dementia onset. An upward SES transition reduced dementia risks and increased the length of dementia-free periods over the life course.
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