Higher cognitive ability in early life linked to lower risk of dementia

General cognitive ability early in life influences later-life risk of cognitive impairment and dementia. An NIA-funded study published in Alzheimer's & Dementia found that adolescent cognition predicted dementia risk in older adulthood, in part through its association with educational attainment. Findings from the study underscore the influence of early life factors on long-term cognitive health.

Previous research has established low educational attainment as a risk factor for dementia. Additionally, other studies have shown a link between early thinking abilities and later dementia. In this new study, a team led by researchers at the University of Southern California attempted to tease apart these factors by analyzing data from the Project Talent Aging Study (PTAS). Project Talent (PT) is a national longitudinal study of adults launched in 1960 when the 377,015 participants were attending high school. The PTAS has followed up on a subset of the original participants, evolving it into a study of aging and health.

As high school students in 1960, PT participants were tested on their cognitive ability. In 2018, a subset of 22,584 of those participants was selected to participate in the PTAS. The PTAS selection process prioritized former students from racially integrated and majority Black schools and included a sample consisting of twins and siblings. Additionally, there was a supplementary effort to increase recruitment of PT participants from diverse backgrounds. PTAS participants were reexamined to assess their cognitive function and proficiency in tasks involving memory and cognition skills, serving as potential indicators of dementia or mild cognitive impairment.

The study was implemented in two stages. In the first stage, 6,491 participants completed a mailed questionnaire that included inquiries about their educational attainment, occupation, and demographics (i.e., age, sex, race, household socioeconomic status indicators in 1960). Only participants who completed the first stage were invited to participate in the second stage. In this next stage, completed by 2,411 participants, they were administered phone-based cognitive tests and completed a web survey about their memory, lifestyle, family, and health.

In their analysis, the researchers found that adolescent cognitive ability predicted both cognitive impairment and dementia in later life. Next, they used statistical modeling to test whether cognitive abilities during adolescence not only directly affected the risk of dementia but also contributed to obtaining higher education and engaging in more complex careers, which, in turn, may decrease risk. They found that those who had high cognitive ability in earlier life, with higher levels of educational attainment, had less risk of cognitive impairment later in life. Although the number of years spent in education was a strong predictor of the participants' occupations, the complexity of those occupations did not have any effect on either cognitive impairment or dementia over and above the strong effect of adolescent cognitive ability.

These results were further supported by analysis of twin pairs who typically share similar levels of overall cognitive ability. When looking at the 82 discordant pairs (one twin with cognitive impairment or dementia and one without), they found their adolescent cognitive ability scores were similar, but differences in education could predict current cognitive impairment status. This indicates that the link between early life cognitive ability and later life cognitive impairment is not simply due to genetic factors or a shared family environment.

Overall, the study's findings suggest an association between adolescent cognitive ability and later-life risk of dementia and cognitive impairment. Additionally, having less education was shown to be a risk factor for dementia, in part due to education's relationship with cognitive ability.

Limitations of the study include the fact that mortality and nonresponse to the later-life PTAS follow-up likely led to a less-representative sample. However, as the initial PT sample was representative of the high school population, the final sample remains considerably more reflective of older adults in the United States compared to a study that relied solely on participants' willingness to engage in later-life research. Also, the twin sample was relatively small.

The study also highlights factors that were not included but could contribute to dementia risk, such as cognitively stimulating leisure time activities, depressive symptoms, and other health conditions. Future research could examine the relationship between general cognitive ability and other factors that influence later life cognitive outcomes.

This research was funded in part by NIA grants U01AG009740, R01 AG043656, R01 AG056163, and RF1 AG056164.

These activities relate to NIH's Alzheimer's and Related Dementias Research Implementation Milestone 1.I, "Identify life course and multi-level mechanisms of and pathways to AD/ADRD inequities and use the discoveries to reduce these inequities."

Reference: Huh J, et al. General cognitive ability in high school, attained education, occupational complexity, and dementia risk. Alzheimer's & Dementia.2024(4):2662-2669. doi: 10.1002/alz.13739.

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