Epidemiology is the study of how often diseases affect different groups of people and the reasons for these patterns. For Alzheimer’s disease, it seeks to understand the distribution and determinants of this condition in populations. Alzheimer’s is a progressive brain disorder that impairs memory, thinking skills, and the ability to carry out simple tasks. By examining large groups, epidemiologists identify characteristics that influence who gets the disease, providing insights into its causes and potential prevention.
Prevalence and Incidence of Alzheimer’s Disease
The statistical footprint of Alzheimer’s is understood through prevalence and incidence. Prevalence is the total number of people living with the disease, while incidence measures the number of new cases diagnosed within a specific time frame. Globally, an estimated 51.6 million people were living with dementia in 2019, with Alzheimer’s accounting for the majority of these cases. This represents a more than doubling of affected individuals since 1990.
The disease’s prevalence increases with age. In Europe, for example, the prevalence is estimated to be just under 1% for those aged 65-74, but it rises to over 7% in the 75-84 age group and exceeds 22% for individuals 85 and older. In the United States, approximately 1 in 9 people aged 65 and older has Alzheimer’s.
The rate of new cases also climbs with age. European data shows an incidence rate of 11.08 per 1,000 person-years, meaning that for every 1,000 people followed for one year, about 11 new cases will be diagnosed. This rate increases almost exponentially until about the age of 85, underscoring the public health challenge as global populations age.
Key Risk Factors
The risk of developing Alzheimer’s is shaped by non-modifiable factors, which cannot be changed, and modifiable ones. The primary non-modifiable risk factors are age and genetics. After age 65, the likelihood of developing the disease approximately doubles every five years.
Genetics also play a part, particularly the apolipoprotein E (APOE) gene. One allele, APOE-e4, is associated with an increased risk for late-onset Alzheimer’s. Having one copy of the APOE-e4 allele can increase risk by three to four times, while two copies may increase it by 10 to 15-fold. Inheriting this allele increases susceptibility but does not guarantee the disease will develop.
Modifiable risk factors are related to lifestyle and health, offering opportunities for intervention. Conditions such as high blood pressure, high cholesterol, and diabetes are risk factors for Alzheimer’s, especially when they occur in midlife. The APOE-e4 gene also has a link to cardiovascular disease, suggesting these factors may have compounding effects.
Other lifestyle elements contribute to risk. Lower levels of formal education have been associated with a greater likelihood of developing dementia. Conversely, engaging in mentally stimulating activities, maintaining a healthy diet, and regular physical activity appear protective. These factors influence “cognitive reserve,” the brain’s ability to withstand neurological damage without showing clinical signs of decline.
Demographic and Geographic Disparities
Disparities in the prevalence and impact of Alzheimer’s exist across demographic and geographic groups. In the United States, older Black Americans are about twice as likely, and older Hispanic Americans are about one-and-a-half times as likely, to have Alzheimer’s compared to white populations.
Gender differences are also apparent, with women having a higher lifetime risk of developing the disease. Nearly two-thirds of Americans with Alzheimer’s are women. This is partly due to women living longer than men, but other biological factors may also be involved.
The reasons for these disparities are complex. They include differences in socioeconomic status and a higher prevalence of the cardiovascular risk factors mentioned earlier in Black and Hispanic communities. Systemic issues, including disparities in access to healthcare and potential biases in diagnosis and management, also contribute.
Geographic location plays a role, with studies showing variations in Alzheimer’s mortality rates between different U.S. regions. For instance, some research indicates higher mortality rates on the West Coast compared to the East Coast. These differences could involve environmental exposures, lifestyle factors, or variations in how causes of death are recorded.
Projected Future Burden
The number of individuals with Alzheimer’s is projected to increase substantially in the coming decades, driven by the aging of the global population. As the large baby boomer generation moves into the highest-risk age group, the number of cases is expected to surge.
Globally, the number of people with dementia was projected to rise from 57 million in 2019 to an estimated 153 million by 2050. In the United States alone, the number of people age 65 and older with Alzheimer’s is forecast to grow from over 7 million today to nearly 13 million by 2050. This increase will place an unprecedented strain on long-term care services and government health programs.
The economic consequences are equally serious. The total cost of care for individuals with Alzheimer’s and other dementias in the U.S. is projected to rise from $384 billion in 2025 to nearly $1 trillion by 2050. These figures do not include the value of unpaid care provided by millions of family members and friends. The escalating burden underscores the urgency of research and public health planning.