amyloid plaques are uncommon in CTE.198-199 How the brain changes associated with CTE are linked to cognitive or behavioral changes is unclear. More research is needed to better understand the relationship between TBI, repeated blows to the head, CTE and Alzheimer’s disease. Overview 17 Other Risk Factors A growing body of evidence indicates that critical illness and medical encounters such as hospitalization in older people increase their risk of long-term cognitive impairment.200-206 The emergence of novel coronavirus disease in 2019 (COVID-19) resulted in more than 1.3 million hospitalizations among U.S. adults age 65 and older between January 1, 2020, and July 24, 2021.207 This has the potential to increase the number of cases of cognitive impairment following critical illness. Furthermore, a number of these individuals will receive or have received mechanical ventilation, which increases one’s risk of delirium,208 an acute state of short-term confusion that is a risk factor for dementia.209-211 There is also rapidly emerging evidence on how exposure to air pollution may be related to dementia risk. A number of different air pollutants have been studied in relation to cognition, cognitive decline and dementia itself. The most consistent and rigorous results concern fine particulate matter air pollution, which consists of tiny solid particles and liquid droplets generated by fuel combustion, fires and processes that produce dust. Higher levels of long-term exposure to fine particulate matter air pollution are associated with worse cognitive decline.164 Researchers are also studying a variety of other risk factors. Among the many being studied are inadequate sleep or poor sleep quality,212-214 excessive alcohol use,215 depression216 and hearing impairment.217 Looking to the Future The relatively recent discovery that Alzheimer’s begins 20 years or more before the onset of symptoms helps explain why it has been difficult to prevent and treat Alzheimer’s disease effectively. However, it also implies that there is a substantial window of time in which we can intervene in the progression of the disease. Scientific advances are likely to help us identify effective methods to prevent and treat Alzheimer’s disease. For example, advances in the identification of biomarkers for Alzheimer’s will enable earlier detection of the disease, giving those affected the opportunity to address modifiable risk factors that may delay cognitive decline and participate in clinical studies of potential new treatments. Biomarker advances may also accelerate the development of these new treatments by enabling clinical trials to specifically recruit individuals with the brain changes experimental therapies target. In addition, biomarker, basic science and other research advances offer the potential to expand the field’s understanding of which therapies may be most effective at which points in the Alzheimer's disease continuum. However, a fuller understanding of Alzheimer's — from its causes to how to prevent it, how to manage it and how to treat it — depends on other crucial factors. Among these is the inclusion of participants from diverse racial and ethnic groups in all realms of Alzheimer's research. The lack of inclusion has several consequences. First, accurately measuring the current and future burden of Alzheimer’s disease in the United States requires adequate data from Black, Hispanic, Asian American/Pacific Islander and Native American communities. The lack of representation is a concern because the populations of older adults from these groups make up nearly a quarter of the older adult population, and that share is projected to grow.218 Second, current data indicate that, compared with non-Hispanic Whites, Blacks and Hispanics are at increased risk for Alzheimer’s (see Prevalence section, page 18). Alzheimer’s research that minimally involves Black and Hispanic participants largely ignores populations who bear the greatest risk. As a result, risk factors common in these populations but less common in non-Hispanic Whites are likely to be poorly understood. Inclusion is more than a matter of enrolling more participants from underrepresented groups. Increasing diversity among researchers and engaging with and seeking input from communities are also important. Improving inclusion in all of these ways expands the range of lived experiences among participants and the extent to which those experiences are known and become topics of investigation.219 Finally, lack of inclusion limits our ability to understand whether and how Alzheimer’s risk factors and interventions work in populations that carry different baseline susceptibility to Alzheimer’s disease. Only by improving representation in clinical trials, observational studies and other investigations will everyone have the potential to benefit from advances in Alzheimer’s science. By 2050, the number of people age 65 and older with Alzheimer's dementia is projected to reach 12.7 million. PREVALENCE Prevalence 19 That is because the risk of dementia increases figure 2 with advancing age. The population of Americans age 65 and older is projected to grow from 58 million in 2021 to 88 million by 2050.220-221 The baby-boom generation (Americans born between 1946 and 1964) has already begun to reach age 65 and beyond,222 the age range of greatest risk of