Incidence refers to the number of new cases of a disorder identified in a specified time period. Prevalence refers to the number of people who are living with the disorder in a given time period.
Worldwide, an estimated 50 million people are living with dementia (World Health Organization [WHO], 2017). These numbers are projected to reach 82 million by the year 2030 and 152 million by 2050, with the majority of individuals coming from low- and middle-income countries (Alzheimer’s Disease International, 2015; WHO, 2017). Globally, the annual number of new cases of dementia is 9.9 million (Alzheimer’s Disease International, 2015). These estimates are approximately 30% higher than the annual numbers reported in 2010 (7.7 million new cases, according to a 2012 report by WHO and Alzheimer’s Disease International).
Within the United States, approximately 5.7 million people are living with dementia (Alzheimer’s Association, 2018; Plassman et al., 2007). Alzheimer’s disease accounts for approximately 60%–70% of these cases, followed by vascular dementias (National Institute on Aging, 2017; WHO, 2017). Similar to the global trends, these numbers are expected to rise as life expectancy increases. The total number of individuals living with Alzheimer’s dementia is projected to be 13.8 million by 2050 (Hebert, Weuve, Scherr, & Evans, 2013). An additional study by Matthews et al. (2018) projects that 13.9 million individuals aged 65 years or older will be diagnosed with Alzheimer’s disease or related dementias in the United States by 2060.
While the number of adults living with dementia in the United States and other countries is expected to grow exponentially by 2050 with increased life expectancy, recent studies suggest that age-specific risk (i.e., the risk of dementia at a specific age) has declined over the past 30 years in some high-income countries, including the United States, England, and the Netherlands (Hudomiet, Hurd, & Rohwedder, 2018; Langa et al., 2017; Matthews et al., 2013; Satizabal et al., 2016; Schrijvers et al., 2012).
A study by Langa et al. (2017) found that the number of new cases of dementia in adults 65 years and older in the United States fell by 24% in a 12-year period—from 11.6% in 2000 to 8.8% in 2012. A corresponding decrease in the number of adults 65 and older living with dementia in the United States (from 12.0% in 2000 to 10.5% in 2012) was reported in a study by Hudomiet and colleagues (2018). This trend may, in part, be due to higher education levels, better access to health care, and improvements in cardiovascular treatments.