Study Finds Slope of Cognitive Decline Not Largely Determined by Adulthood Factors

Cognitive functioning (CF) declines as a person ages, according to a recent study published in PLoS ONE; however, when measuring non-age-related variation in CF, investigators determined that controlled factors (socioeconomic, physical health) are not significantly associated with CF.

“We found all the observed individual socioeconomic indicators, bio-behaviors, and physical health measures could not explain the within-person non-age-related variability in CF from age 54 to 85,” the study authors wrote.

The investigators observed that age-related change in CF vary due to socioeconomic and health factors, although early life conditions still did not appear to significantly impact CF as they entered later life.

It is estimated that dementia will affect 131.5 million people globally by 2050. Dementia, Alzheimer disease, cerebrovascular disease, and Lewy body disease is estimated to account for 41% of cognitive decline in an aging population, but 59% of these cases are not going to be one of the aforementioned conditions; however, they will affect mortality, morbidity, and quality of life.

Investigators sought to determine how and why the overall decline of cognitive abilities occurs at different rates in people.

“Solving this problem has important ramifications for policymakers and medical interventions to target the causes that are most influential on cognitive trajectories,” the study authors wrote.

The team used nationally representative data of individuals aged 54 to 85 years taken from the US Health and Retirement Study (HRS), conducted between 1996 and 2016. They studied the relationship between a wide range of factors, such as adult socioeconomic status or bio-behavioral factors, and long-term cognitive trajectory (slope) of decline. They conducted follow-up after 20 years to model the slopes of CF factors.

The data suggest that individual socioeconomic status—including education, income, race, and wealth—was the most important observable factor that determined variation of CF among people aged 54 years. Observed factors accounted for 38% of the CF variation in this younger study population.

But controlled factors only accounted for 5.6% of between-person variation in age slope, whereas 23% of within-person CF variation was explained by age. Additionally, it was noted that having a college degree was associated with age slope, but years of education were not necessarily associated with CF slope.

Study limitations included that HRS scores could be influenced by the floor effect; the HRS focuses on memory function more than other cognitive domains, such as processing speed or executive function, and the study did not measure certain factors that can predicate a person’s CF trajectory.

“Although many factors are statistically associated with the level and slope of CF, their contributions to the population variation, especially the slope, are rather small,” the investigators wrote. “Future research is urgently needed to discover the main determinants of the slope of decline to slow down the progression of cognitive impairment and dementia.”

Reference

Zheng H, Cagney K, Choi Y. Predictors of cognitive functioning trajectories among older Americans: A new investigation covering 20 years of age- and non-age-related cognitive change. PLoS ONE. February 8, 2023. Accessed February 9, 2023.