A new study published Monday in JAMA Neurology identified eight risk factors that were linked to 36.9% of Alzheimer's cases and related dementia in the United States—findings that signal a change in the most significant Alzheimer's and dementia risk factors over the past decade.

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Study details and key findings

For the study, researchers collected data from 378,615 participants in CDC's 2018 Behavioral Risk Factor Surveillance System. For each risk factor, they extracted relative risks from recent meta-analyses.

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The study's self-reported race and ethnicity data identified 6,671 American Indian and Alaska Native participants, 8,043 Asian participants, 29,956 Black participants, 28,042 Hispanic participants, and 294,394 white participants.

According to study co-authors Roch Nianogo of the University of California, Los Angeles, and Deborah Barnes of the University of California, San Francisco, eight modifiable risk factors were associated with 36.9% of Alzheimer's and dementia cases. For each of the eight factors, the population-attributable risk was:

• Hearing loss: 2.3%
• Current smoking: 6.0%
• Diabetes: 7.3%
• Depression: 8.5%
• Midlife hypertension: 8.8%
• Low education: 11.7%
• Physical inactivity: 11.8%
• Midlife obesity: 17.7%

Among all participants, midlife hypertension and midlife obesity were the most prevalent risk factors. However, prevalence varied across race and ethnicity.

In addition, risk factor association with Alzheimer's and dementia varied by race and ethnicity. For example, midlife obesity had the highest association with Alzheimer's and dementia among Black (21.7%), American Indian and Alaska Native (20.3%), and white (17.3%) populations.

Among Hispanic participants, low educational attainment was the most prevalent risk factor (26.5%), while physical inactivity was the highest association in Asian participants (9.5%).

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Overall, combined population-attributable risks were higher in men (35.9%) than in women (30.1%). However, risk associated with depression was higher in women (10.5%) than in men (6.4%).

Commentary

According to the study's authors, the findings suggest that the most significant modifiable risk factors linked to Alzheimer's and dementia have changed over the past decade.

"We published a similar study a little more than 10 years ago, and the most important risk factors then were physical inactivity, depression, and smoking," Barnes told MedPage Today.

"Today, the top three risk factors are midlife obesity, physical inactivity, and low education," Barnes explained. "This is important because it suggests that the growing number of people who are obese in the U.S. could have a major long-term impact on dementia rates."

"Our results also highlight the importance of making sure everyone in our country gets adequate education," she added. "COVID-19 had a devastating impact on education and graduation rates and it will be important to help those students get caught up. This is especially true in Hispanic individuals, where low education is the biggest risk factor."

Since there is currently no effective cure for Alzheimer's and dementia, Nianogo emphasized the importance of prevention. He suggested that risk reduction strategies may have more of an impact if they target higher-prevalence risk factors.

"Understanding which risk factor plays a role in accelerating cognitive decline can help providers and individuals be proactive in addressing these risk factors early in their lifetime," Nianogo told MedPage Today. "We also wanted to understand what that meant for different subpopulations defined by sex and race and ethnicity, as this can be important for designing tailored and targeted interventions."

Ultimately, Nianogo noted that "[i]t's important to note that these findings were mostly based on observational studies."

"While they could reflect what is really happening, they could also reflect the effect of other factors not accounted for in our study," he acknowledged. "More rigorous study designs are needed to shed more light on this important issue." (George, MedPage Today, 5/9)