In the U.S., 40 Percent of All-Cause Dementia Is Preventable

How much all-cause dementia could be prevented in the United States? In the July 6 JAMA Open, researchers led by Mark Lee, University of Minnesota, Minneapolis, attributed 41 percent of dementia cases to 12 modifiable lifestyle factors. Obesity, high blood pressure, and lack of exercise accounted for the lion’s share. The percentage of preventable dementia cases was higher among black and Hispanic than among Caucasian and Asian Americans. “These findings can guide prevention efforts by highlighting the risk factors most consequential for U.S. dementia cases,” Lee wrote to Alzforum.

  • In the U.S., 12 lifestyle factors explain 41 percent of dementia cases.
  • Obesity, hypertension, and physical inactivity accounted for half the modifiable risk.
  • Preventable dementia is more common in people of color.

This estimate is on par with a Lancet Commission report linking 40 percent of dementia cases worldwide to the same 12 risk factors: physical inactivity, excess alcohol consumption, obesity, smoking, hypertension, diabetes, depression, traumatic brain injury, hearing loss, few years of education, social isolation, and air pollution. However, the report pegged hearing loss, education, and smoking as the three largest ones (Aug 2020 conference news). Lee’s work highlights the epidemiological differences between the United States and other countries.

Lee, who is also first author on the paper, analyzed health surveys among Americans ages 25 to 95 who took part in four large observational cohorts: the American Community Survey; the National Health and Nutrition Examination Survey; the National Health Interview Survey; and the National Social Life, Health, and Aging Project. Air pollution data came from the Center for Air, Climate, and Energy Solutions.

Lee focused on the same 12 lifestyle factors identified by the Lancet Commission. He used the report’s values for relative risk of dementia to figure out the population attributable fraction (PAF), i.e., what proportion of dementia in cohorts is explained by each risk factor.

In the U.S. data, the three most prevalent factors—obesity, hypertension, physical inactivity—also had the largest PAF, each accounting for 20 percent of dementia risk (see image below). Other common risk factors carried lower risk. Air pollution ranked fifth in prevalence but came in second to last as a risk factor, explaining only 2.2 percent of preventable dementia. Excessive alcohol consumption, defined as drinking more than 14 standard drinks per week, accounted for 0.7 percent. These “unweighted” numbers did not take into account that some risks correlate with each other. For example, physical inactivity increases a person’s chances of gaining weight or having high blood pressure, or obesity increases a person's odds of developing diabetes.

Top Threat. High blood pressure, obesity, and lack of exercise account for largest fractions of population-attributable risk for dementia in the United States. PAFs estimate how many people have a disease due to a given risk factor by integrating how common it is and how strongly it associates with disease. Commoner risk factors that closely associate with disease have a higher PAF. [Courtesy of Lee et al., JAMA Open, 2022.]

Adjusting for such correlations, Lee calculated that each factor directly explained 0.5 to 7.0 percent of the total modifiable risk. Obesity, hypertension, and physical inactivity still came out on top, each accounting for about 7.0 percent. Diabetes was a close fourth, at approximately 4.5 percent.

When breaking down the data by self-reported race, people of color generally had a higher risk of preventable dementia. Lee attributed 46.7 percent of dementia risk in Hispanic and 45.6 percent in black survey respondents to the 12 risk factors together, compared to 39.4 and 35.8 percent in Caucasians and Asians, respectively. A higher prevalence of certain risk factors explained the higher risk. For example, 27 percent of Hispanics had fewer than 12 years of education compared to 5.5 percent of Caucasians, accounting for 14 percent and 3 percent of their all-dementia risk, respectively. “Identifying the primary drivers of dementia burden within different racial and ethnic groups is a critical precursor to crafting policies with an equitable health impact,” the authors wrote.

Deborah Barnes, University of California, San Francisco, and colleagues recently found much the same in about 380,000 American adults who answered the U.S. Behavioral Risk Factor Surveillance Survey (Nianogo et al., 2022). Eight dementia risk factors—physical inactivity, midlife obesity, smoking, midlife hypertension, diabetes, depression, hearing loss, and few years of education—correlated to 37 percent of dementia risk in the United States, with obesity, physical inactivity, and few years of education topping the charts. Blacks, Hispanics, and American Indians/Alaska Natives had higher prevalence of risk factors than Caucasians or Asians.

Reducing exposure to these modifiable risk factors could reduce dementia prevalence. Indeed, the National Plan to Address Alzheimer’s Disease calls for lowering risk factor prevalence by 15 percent by 2023 (Dec 2021 news). Lee calculated that if that was done for each of the 12 factors reported here, dementia cases would drop in the United States by 7.3 percent, or about 427,000 people. “Prevention by reducing modifiable risk factors is currently the most important tool in our toolbelt for curbing dementia cases,” wrote Lee. “Finding ways to reduce how many people have these risk factors could lead to a significant reduction in the number of Americans living with dementia.”—Chelsea Weidman Burke

Comments

  1. This is a refreshing paper reminding the scientific community, the policymakers, and the public of the importance of prevention. If approximately 40 percent of dementia cases are associated with exposure to 12 modifiable risk factors, a lot can be done to modify the future.

    The results do not surprise me, as they have strong face validity and make a lot of common sense. The racial and ethnic differences are novel but consistent with the patterns observed for other diseases.

    The results of this study remind us that investing some of our societal money in improving education, improving general living conditions (e.g., facilitating physical exercise), and strengthening the primary prevention of common chronic diseases (e.g., hypertension and obesity) may be more prudent than putting all of our resources toward the search for a magic treatment for Alzheimer's disease or the development of expensive and invasive biomarkers to predict the future occurrence of the disease. Public health research may be a better investment than mechanistic research for the future health of the general population.

    For the United States, in particular, the priority is to intervene with the three most impactful risk factors: physical inactivity, obesity, and hypertension. Unfortunately, these three risk factors often co-occur in the same individuals and can act synergistically. Once again, the solution is not a magic treatment but a slow and painful transformation of dietary habits and lifestyles. Dietary changes may require complex interventions at the individual level (e.g., nutritional education of children or teaching people how to prepare healthy food) and economic transformations (e.g., control and regulation of the production, advertisement, and sale of food). Some of the needed interventions may require dramatic political and economic decisions. 

    As clearly indicated by the authors, the next step is to develop intervention trials to demonstrate whether, and to which extent, modifying the risk factors alone or in combination does reduce the risk of dementia. A similar trial involving a multidomain intervention was conducted recently in Finland (FINGER trial). For some of the interventions, a formal trial may not be possible and observational data can be used. For example, a study of changes in the risk of dementia over time may reflect the effectiveness of an intervention at the population level.

    View all comments by Walter A. Rocca

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References

News Citations

  1. Lancet Commission’s Dementia Hit List Adds Alcohol, Pollution, TBI
  2. HHS Adds Goal of Alzheimer’s Prevention to National Plan

Paper Citations

  1. Nianogo RA, Rosenwohl-Mack A, Yaffe K, Carrasco A, Hoffmann CM, Barnes DE. Risk Factors Associated With Alzheimer Disease and Related Dementias by Sex and Race and Ethnicity in the US. JAMA Neurol. 2022 Jun 1;79(6):584-591. PubMed.

External Citations

  1. American Community Survey
  2. National Health and Nutrition Examination Survey
  3. National Health Interview Survey
  4. National Social Life, Health, and Aging Project
  5. Center for Air, Climate, and Energy Solutions
  6. U.S. Behavioral Risk Factor Surveillance Survey

Further Reading

Primary Papers

  1. Lee M, Whitsel E, Avery C, Hughes TM, Griswold ME, Sedaghat S, Gottesman RF, Mosley TH, Heiss G, Lutsey PL. Variation in Population Attributable Fraction of Dementia Associated With Potentially Modifiable Risk Factors by Race and Ethnicity in the US. JAMA Netw Open. 2022 Jul 1;5(7):e2219672. PubMed.

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