Abstract 
 
 Importance The aging of the US population is expected to lead to a large increase in the number of adults with dementia, but some recent studies in the United States and other high-income countries suggest that the age-specific risk of dementia may have declined over the past 25 years. "The fact that our study also shows a decline [in the prevalence of dementia], provides additional evidence that this phenomenon seems to be going on across the United States and not in one particular geographic region." More years of education was associated with a lower risk for dementia, and average years of education increased significantly (from 11.8 years [95% CI, 11.6-11.9 years] to 12.7 years [95% CI, 12.6-12.9 years]; P < .001) between 2000 and 2012. For instance, a recent population-based study8 of dementia in England found a 24% decline in the expected number of cases of dementia between 1991 and 2011 (a 6.5% prevalence among older adults in 2011, compared with 8.3% in 1991; P = .003), which translates to more than 200 000 fewer cases of dementia. Quiz Ref IDThere have been changes over the past 2 to 3 decades in both the prevalence and treatment of cardiovascular risk factors that also influence the risk for dementia. For instance, 23% of US adults were obese in 1990 compared with 35% in 20129,10; among adults 65 years or older, the prevalence of diabetes increased from 9% to 21%.10 However, intensity of treatment for diabetes, hypertension, and high cholesterol level has increased with more patients achieving treatment goals, and a significant decline in the vascular complications of diabetes such as heart attack, stroke, and lower-extremity amputations,11 suggesting that there could be a “spill-over” benefit of a decline in the vascular-related risk for dementia.4,7 
 
 Rising levels of education among US adults over the past 25 years may also have contributed to decreased dementia risk. The proportion of adults 65 years or older with a high school diploma increased from 55% in 1990 to 80% in 2010, while the proportion with a college degree increased from 12% to 23%.12 More years of formal education is associated with a reduced risk of dementia, likely through multiple causal pathways, including a direct effect on brain development and function (ie, the building of “cognitive reserve”), health behaviors, as well as the general health advantages of having more wealth and opportunities.13-15 
 
 To further address these questions, we used the Health and Retirement Study16 (HRS), a large nationally representative prospective cohort study of US adults, to test whether the age-specific prevalence of dementia declined in the United States between 2000 and 2012. The study used data gathered in two snapshots, one in 2000 and another in 2012, that each looked at more than 10,000 Americans who were at least 65 years old. For respondents represented by a proxy, an 11-point scale was developed using the proxy’s assessment of the respondent’s memory ranging from excellent to poor (score, 0-4), the proxy’s assessment of whether the respondent had limitations in 5 instrumental activities of daily living (IADLs) (managing money, taking medication, preparing hot meals, using phones, and shopping for groceries; score, 0-5), and the survey interviewer’s assessment of whether the respondent had difficulty completing the interview because of a cognitive limitation (a score of 0-2 indicating, none, some, and prevents completion). Table 4 reports the results of 4 different logistic regression models with the presence of dementia as the outcome variable, using pooled 2000 and 2012 data. Discussion 
 
 In a large nationally representative survey of older Americans we found that, among those 65 years or older, the prevalence of dementia decreased from 11.6% to 8.8% between 2000 and 2012, representing an absolute decrease of 2.8 percentage points, and a relative decrease of about 24%. Educational attainment increased significantly, with those 65 years or older in 2012 having nearly 1 additional year of education compared with the 2000 cohort. After controlling for the socioeconomic factors of education, wealth, and race/ethnicity, controlling for changes in the prevalence of cardiovascular risk factors did not explain much of the additional difference in dementia risk across the two cohorts. Our study, along with prior studies, supports the notion that “cognitive reserve” resulting from early-life and lifelong education and cognitive stimulation may be a potent strategy for the primary prevention of dementia in both high- and low-income countries around the world.21 However, it should be noted that the relationships among education, brain biology, and cognitive function are complex and likely multidirectional; for instance, a number of recent population-based studies have shown genetic links with level of educational attainment,22,23 and with the risk for cognitive decline in later life.24 Higher levels of educational attainment are also associated with health behaviors (eg, physical activity, diet, and smoking), more cognitively-complex occupations, and better access to health care, all of which may play a role in decreasing lifetime dementia risk. However, the full set of social, behavioral, and medical factors contributing to the decline in dementia prevalence is still uncertain. Back to top Article Information 
 
 Corresponding Author: Kenneth M. Langa, MD, PhD, Division of General Medicine, University of Michigan, 2800 Plymouth Rd, Building 16, Room 430W, Ann Arbor, MI 48109-2800 (klanga@umich.edu). Put in more human terms, "that's well over a million people who don't have dementia, who would have had it if the rates had stayed the same as 2000 rates," says John Haaga, who directs the Division of Behavioral and Social Research at the National Institute on Aging, which funded the study.
– Good news for older Americans: A new study suggests that their odds of getting dementia are shrinking despite predictions to the contrary. While standardized tests showed 11.6% of Americans 65 and older had dementia in 2000, only 8.8% did in 2012, reports NBC News. What's more, people are getting dementia later, with the average age at diagnosis increasing from 80.7 to 82.4 over the same period, reports the New York Times. One possible factor: A person's average education increased during that period from 11.8 years to 12.7 years, say University of Michigan researchers. "Education might actually change the brain itself," lead author Kenneth Langa tells NPR. "We think that it actually creates more, and more complicated, connections between the nerve cells so that you're able to keep thinking normally later into life." Another potential factor: While health ailments linked to dementia such as diabetes, high blood pressure, and high cholesterol increased, people were treating them with better medications. The study draws on long-range data about 20,000 Americans from all kinds of backgrounds, and Langa says it suggests that dire predictions about the nation's dementia problem might have been been overstated. The Alzheimer's Association isn't so sure: Though dementia rates may be falling, "the total number of Americans with Alzheimer's and other dementias is expected to continue to increase dramatically" as the number of older adults climbs," it says. In the US, the number of people 65 and older is projected to double by 2050, notes NPR. (A game could reduce your dementia risk.)