Study of 7,068 elderly Americans suggests more research is needed to inform healthy ageing strategies

A new analysis explores relative statistical associations between various life factors and cognitive decline in elderly Americans, highlighting gaps in knowledge needed to reduce cognitive decline. Hui Zheng of the Ohio State University, U.S., and colleagues present these findings in the open-access journal PLOS ONE on February 8, 2023.

Millions of elderly Americans experience cognitive decline. However, only about 41 percent of this decline can be statistically accounted for by dementia—abnormal decline caused by such conditions as Alzheimer's disease, cerebrovascular disease, and Lewy body disease. Prior research has identified many other factors that may also contribute to cognitive decline, from genetics to early life nutrition, but their relative impacts remain unclear. 

To shed new light, Zheng and colleagues analyzed data from 7,068 American adults born between 1931 and 1941 who were part of a larger study—the Health and Retirement Study—that regularly measured their cognitive function from 1996 to 2016. The study also collected extensive information on personal factors that could contribute to cognitive decline, such as socioeconomic factors, physical health measures, and behaviors including exercise and smoking.

Together, the many factors considered in the study statistically accounted for 38 percent of the variation between participants in their level of cognitive function at age 54. Among those factors, personal education, race, household wealth and income, occupation, level of depression, and parental education were the biggest statistical contributors to that population-level variation, with early life conditions and adult behaviors and diseases contributing less. 

However, all of the considered factors accounted for only 5.6 percent of the variation in how participants' cognitive function changed with age.

Unlike many prior studies, this study also distinguished between age-related cognitive decline and cognitive decline that is unrelated to getting older. Age accounted for 23 percent of the variation in how cognitive function changed from age 54 to 85, but the remaining 77 percent could not be statistically accounted for by the many factors considered.

These findings suggest that more research is needed to identify the major factors contributing to rate of cognitive decline, which could help inform medical treatments, policies, and equity-based strategies to slow decline. 

Hui Zheng adds: "Adulthood socioeconomic conditions have a predominant role in shaping the level of cognitive functioning. 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."

Kathleen Cagney adds: "Understanding cognitive health, and cognitive decline, is paramount.  We must take the long view, with attention to the timing and nature of life experiences, if we are to gain fundamental insights that can inform care and treatment."