Age is the single biggest factor determining who gets dementia, with rates climbing steeply after 70. About 5% of people in their 70s have dementia, roughly 24% of those in their 80s, and over 37% of people 90 and older. But age only tells part of the story. Sex, race, genetics, and several health conditions all shift the odds significantly.
Age Is the Strongest Risk Factor
Dementia is rare before 65 and increasingly common after. Data from the Aging, Demographics, and Memory Study show just how sharply prevalence rises with each decade of life:
- Ages 71 to 79: about 5% have dementia
- Ages 80 to 89: about 24%
- Age 90 and older: about 37%
That steep curve means most people living with dementia are in their late 70s and beyond. Globally, around 57 million people had dementia as of 2021, and the number is rising as populations age worldwide.
Young-Onset Dementia Is Uncommon but Real
Dementia can develop before age 65, though it accounts for only about 3% of all cases in the United States. An estimated 175,000 Americans are living with young-onset dementia. Globally, the figure is around 3.9 million people between the ages of 30 and 64. These cases are often caused by different underlying conditions than typical late-life Alzheimer’s, including frontotemporal dementia, which disproportionately affects people in their 40s and 50s.
Women Are Diagnosed More Often Than Men
About two-thirds of people diagnosed with dementia and Alzheimer’s disease are women. Part of this is straightforward: women live longer on average, and age is the top risk factor. But the gap isn’t just about lifespan.
Research tracking large groups over time shows that dementia rates for men and women are nearly identical through the early 80s. After that, rates in women pull away sharply. By ages 85 to 90, the difference is statistically significant. For Alzheimer’s disease specifically, the divergence starts even earlier, around age 80. In one large study, 25% of women developed dementia compared to about 19% of men. Hormonal changes after menopause, differences in brain structure, and longer exposure to certain risk factors are all thought to play a role, though the exact reasons remain an active area of investigation.
Race and Ethnicity Shape Risk in the U.S.
In the United States, dementia rates are not evenly distributed across racial and ethnic groups. Black Americans are roughly twice as likely, and Hispanic Americans about 1.5 times as likely, to develop Alzheimer’s and related dementias compared to white Americans of the same age.
These disparities are not primarily genetic. They reflect decades of unequal access to healthcare, higher rates of conditions like high blood pressure and diabetes, differences in educational opportunity, and the long-term biological effects of chronic stress and discrimination. Adding to the problem, research shows that Black and Hispanic Americans with dementia are less likely to have received a formal diagnosis from a physician, which delays treatment and support.
Over 60% of the world’s dementia cases occur in low- and middle-income countries, where access to diagnosis, treatment, and caregiving support is limited. Geography and income shape dementia outcomes on a global scale, not just within individual countries.
Genetics Can Multiply the Risk
The gene with the most well-known connection to Alzheimer’s is called APOE. Everyone carries two copies of this gene, and one version, the e4 variant, raises risk considerably. Carrying one copy of the e4 variant doubles or triples your risk of developing Alzheimer’s. Carrying two copies increases the risk 8 to 12 times.
About 25% of people carry at least one copy of the e4 variant. Having the gene does not guarantee you will develop dementia, and many people who get Alzheimer’s don’t carry it at all. But it does help explain why dementia sometimes clusters in families. Rarer genetic mutations can cause early-onset forms of Alzheimer’s that run in families and appear as early as the 30s or 40s, though these account for a very small fraction of total cases.
High Blood Pressure and Diabetes Raise the Odds
Certain chronic health conditions significantly increase dementia risk, and they happen to be conditions that affect some populations more than others. In a large analysis from the All of Us research program, hypertension showed the strongest association with dementia of any factor studied, with people who had high blood pressure nearly six times more likely to develop the condition. Type 2 diabetes doubled the risk.
These are not small effects. Midlife hypertension, meaning high blood pressure in your 40s and 50s, appears especially harmful. The damage to blood vessels in the brain accumulates over years, reducing blood flow and making neurons more vulnerable. Because hypertension and diabetes are more common in Black and Hispanic Americans, and in people with lower incomes, these conditions help explain much of the racial and socioeconomic gap in dementia rates.
Education and Cognitive Reserve
People with fewer years of formal education develop dementia at higher rates. This relationship holds across countries and cultures. Research from the Health and Retirement Study and its international counterparts found that more years of education were associated with a delayed onset of the accelerated cognitive decline that precedes Alzheimer’s.
The leading explanation is a concept called cognitive reserve. Education, mentally stimulating work, and lifelong learning build denser neural connections, giving the brain more backup pathways to rely on as age-related damage accumulates. Someone with high cognitive reserve can tolerate more physical brain changes before symptoms appear. This doesn’t mean educated people never get dementia. It means the threshold for noticeable symptoms is higher, and the onset tends to come later. Conversely, people who had limited access to education, often due to poverty or discrimination, face a compounding disadvantage: higher rates of the chronic diseases that cause dementia, plus less cognitive reserve to buffer against them.
Who Is Most Affected Overall
The people most likely to develop dementia sit at the intersection of several overlapping risk factors. An 85-year-old Black woman with a history of high blood pressure, diabetes, and limited formal education faces a substantially higher risk than a 70-year-old white man with none of those conditions. No single factor determines who gets dementia, but the risks stack. Age provides the foundation, and everything else builds on it.
Many of the strongest risk factors, including high blood pressure, diabetes, and physical inactivity, are modifiable. Managing blood pressure in midlife, controlling blood sugar, staying physically and mentally active, and maintaining social connections all reduce dementia risk meaningfully. The people most affected by dementia are often those with the least access to the resources that could help prevent it.