How much dementia is preventable in the United States? On July 6 in JAMA Open, researchers led by Mark Lee, of the University of Minnesota, Minneapolis, attributed 41 percent of dementia cases to 12 modifiable lifestyle factors. Obesity, high blood pressure and physical inactivity accounted for the lion's share. "These findings could guide prevention efforts by highlighting the risk factors that most influence dementia cases in the United States," Lee wrote to Elsforum.
This estimate is consistent with the Lancet Commission report linking 40% of dementia cases worldwide to the same 12 risk factors: physical inactivity, excessive alcohol consumption, obesity, smoking, hypertension, diabetes, depression, traumatic brain injury, hearing loss, number of years of education, social isolation, and air pollution. However, the report determined that hearing loss, education, and smoking were the three most significant factors (Conference News August 2020).
Lee's work highlights the epidemiological differences between the United States and other countries.
Lee, who is also the paper's first author, analyzed health surveys of Americans ages 25 to 95 who participated in four large observational groups: the American Community Survey; the National Health and Nutrition Examination Survey; the National Health Interview Survey; and the National Project on Social Life, Health, and Aging. The 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 conference. He used the report's values for relative risk of dementia to figure out the population attributable fraction (PAF), that is, what proportion of dementia in groups is explained by each risk factor.
In the US data, the three most common factors – obesity, high blood pressure, physical inactivity – also had the largest PAF, each accounting for 20% of the risk of dementia. Other common risk factors carried lower risks. Air pollution ranked fifth most common but came in second last as a risk factor, explaining only 2.2% of preventable dementia. Excessive alcohol consumption, defined as drinking more than 14 standard drinks per week, accounted for 0.7%. These “unweighted” numbers did not take into account that some risks overlap. For example, physical inactivity increases a person’s chances of gaining weight or having high blood pressure, or obesity increases a person’s chances of developing diabetes.
"Identifying the primary drivers of dementia burden within different racial and ethnic groups is a critical precursor to creating policies that have an equitable impact on health," the authors wrote.
Deborah Barnes, of the University of California, San Francisco, and her colleagues recently found the same thing in about 380,000 American adults who responded to the US Risk Factors Survey (Nianogo et al., 2022). Eight risk factors for dementia – physical inactivity, midlife obesity, smoking, midlife hypertension, diabetes, depression, hearing loss, and years of education – were correlated with 37% of the risk of dementia in the United States, with obesity, physical inactivity, and years of education at the top of the list.
Reducing exposure to modifiable risk factors could reduce the incidence of dementia. Indeed, the National Alzheimer’s Disease Action Plan calls for reducing the incidence of risk factors by 15 percent by 2023 (December 2021 News). Lee calculated that if this were done for each of the 12 factors reported here, dementia cases in the United States would fall by 7.3 percent, or about 427,000 people. “Prevention by reducing modifiable risk factors is now the most important tool in our toolbox for curbing dementia cases,” Lee wrote. “Finding ways to reduce the number of people who have these risk factors could lead to a significant reduction in the number of Americans living with dementia.”
