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  • Cognitive decline naturally occurs as we age, with a common belief that dementia is the cause in most cases.
  • Researchers at the Ohio State University say there are more factors causing cognitive decline than we once thought.
  • Socioeconomic factors, physical health measures, and behaviors, including exercise and smoking, accounted for 38% of the variation between participants in their level of cognitive function at age 54, researchers reported.

Cognitive or mental decline — a deterioration in functions such as the ability to think, remember, understand, and learn — naturally occurs as we age.

Generally speaking, most people associate cognitive decline with dementia diseases such as Alzheimer’s disease.

However, only about 41% of this decline can be accounted for by dementia. A number of risk factors that may also contribute to cognitive decline, including socioeconomic status, education, race, physical health measures, and behaviors such as exercise and smoking, have previously been identified. But researchers at The Ohio State University and the University of Michigan have now found that these factors only account for a small amount of the variation in mental abilities among older people highlighting gaps in the knowledge needed to reduce cognitive decline.

The study appears in the journal PLoS ONE.

For this study, the research team applied a statistical approach to examine associations between various lifestyle factors and cognitive decline in older Americans.

“Prior studies have produced some mixed findings regarding some determinants of cognitive functioning, which could come from different datasets, research designs, time periods, and countries,” Dr. Hui Zheng, professor in the Department of Sociology at The Ohio State University, and lead author of this study explained to Medical News Today.

“They may also stem from the fact that each individual study only assessed a limited number of predictors without accounting for intercorrelations with unobserved confounders,” he continued. “They also tend to have a narrow-age cohort or short follow-up. Moreover, we want to effectively estimate both the statistical significance and the substantive contribution of the predictors of cognitive trajectory.”

Dr. Zheng and his team analyzed data from over 7,000 American adults born between 1931 and 1941 who had participated in a larger study called the Health and Retirement Study where their cognitive function had been regularly measured from 1996 to 2016.

The Health and Retirement Study also collected information on participants’ lifestyle behaviors, including exercise, smoking, physical health, and socioeconomic factors such as education, income, and occupation.

Upon analysis, the research team found the many factors included in the study statistically accounted for only 38% of the variation between participants in their level of cognitive function at age 54. They found the factors with the biggest effect included personal education, household wealth and income, race, occupation, level of depression, and parental education.

“These could be linked through material, psychosocial, and neuropathologic mechanisms,” Dr. Zheng said when explaining how these factors could contribute to cognitive decline. “For example, education can improve cognitive reserve and delay the manifestation of neuropathology that occurs as a result of aging-related or pathologic process.”

The factors with the least effect on cognitive decline included early life conditions and adult behaviors and diseases. In addition, interestingly, these factors accounted for only 5.6% of the variation in how cognitive function declined in people aged between 54 and 85.

Dr. Zheng said they were a bit surprised at the factors statistically accounting for 38% as they had included a wide range of factors.

“One thing I want to emphasize is that individual socioeconomic status (e.g., education, income, wealth, occupation, race, parental education) matters a lot,” he added. “These findings point to the predominant importance of socioeconomic conditions in shaping the level of cognitive functioning.”

MNT spoke with Dr. David A. Merrill, a psychiatrist, and director of the Pacific Neuroscience Institute’s Pacific Brain Health Center at Providence Saint John’s Health Center in Santa Monica, CA, about this study. He said the presumption has been that individual choices and behaviors matter “the most” in terms of maintaining intact cognitive function with aging.

“However, this study raises the possibility that social determinants of health may play as important, if not more important role, in determining the odds of achieving successful aging outcomes, including maintaining normal memory into and throughout older adulthood,” Dr. Merrill said.

Dr. Karen D. Sullivan, a board certified neuropsychologist and creator of the I CARE FOR YOUR BRAIN education program, said what brain scientists now understand about cognitive aging is that it is multiple decades-long processes that come together to determine one’s chances of having cognitive decline.

“Socioeconomic factors, vascular health, and health behaviors all come together in the individual and interact with genetic predispositions to establish our brain health as an older adult,” Dr. Sullivan explained to MNT.

“Socioeconomic factors, in particular the quality and quantity of one’s early education, exerts an influence on future cognitive health through the contribution to cognitive reserve,” she added. “Cognitively complex activities contribute to our ‘brain bank’ by building layers and layers of neural networks that can better withstand future neurodegeneration.”

MNT asked Dr. Sullivan how these findings might help doctors slow the rate of cognitive decline in people.

“Brain health is whole-person health,” she answered. “The idea that focusing on only one aspect of health, like diet or exercise, will result in a healthy older brain is naïve. Science, as reported in this study, makes it clear we need to make sustained efforts across all aspects of wellness to remain cognitively vibrant into old age.”

“Brain health should be important to us across the lifespan — not just when we hit 65,” she continued. “Brain health is cumulative and what we do in earlier phases of development matters in terms (of) who experiences cognitive decline and who does not. We can either decide to have a cumulative advantage or disadvantage — we get to decide with our behaviors.”

Dr. Merrill said these findings draw attention to the important and urgent need of our society at large to structure itself in ways that promote healthy behaviors as the default for not just the lucky few born into wealth, but for all of us as members of a larger interdependent community.

“We need to make common sense health behaviors like resources for getting regular physical exercise and having access to nutritious foods the expected norm for all, not the few,” he added.

And Dr. Merrill commented the study draws attention to the importance of an individual’s education as protective against cognitive decline with aging.

“I highly encourage my patients and their loved ones to pursue life-long learning on topics they find interesting and enjoyable,” he explained. “For me, brain health is a topic that we can study together as patient and provider. Every clinic appointment is an opportunity for bi-directional learning and shared decision-making about what to do towards improving a person’s body and brain health.”