Right now nearly 6.5 million Americans age 65 and older are estimated to be living with Alzheimer’s, the most common type of dementia, and by 2050 that figure is projected to roughly double. Today, nearly half of older adults (those over age 67) die with or from Alzheimer’s or another form of dementia. That’s more than the fatalities from breast and prostate cancer combined, and is up 36% from 20 years ago. Undiagnosed early-onset dementia in people under 65, and sometimes significantly younger, is also on the rise.

These numbers are startling, especially given that Alzheimer’s remains in many regards shrouded in mystery. Who is most likely to develop the disease, the nature of its progression and what constitutes effective treatment are all poorly understood. But a promising new area of research is bringing much-needed clarity to these pressing questions.

The causes of Alzheimer’s are elusive. Both Alzheimer’s and related dementias (ADRDs) are linked to the aging brain, but aging is not the direct cause of either one. Researchers point to family history, since those with a parent or sibling with the disease seem more likely to develop it. But less than 1% of Alzheimer’s cases are caused by rare deterministic genes that cause the disease. Perhaps the most commonly held theory is that Alzheimer’s is caused by a buildup of the proteins amyloid or tau in the brain, causing plaques around brain cells or tangles within them. But several studies, including recent research with mice, have challenged that theory, while other studies have shown that people with amyloid plaque buildup may never develop ADRDs.

Both Alzheimer’s and related dementias (ADRDs) are linked to the aging brain, but aging is not the direct cause of either one.

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According to research, nearly two-thirds of the millions of Americans living with ADRDs are women. And while white people make up the majority of those with Alzheimer’s and dementia, African Americans are twice as likely as whites to have ADRDs, while people identifying as Hispanic are about one and a half times more likely than non-Hispanic whites. But these numbers are misleading: Studies consistently show that Black and underrepresented patients are less likely to be diagnosed in the early stages of dementia; the disease is then discovered later, when it is more advanced. Biases in the diagnostic thresholds providers apply to their patients during screenings are widespread.

Black and underrepresented patients are less likely to be diagnosed in the early stages of dementia; the disease is then discovered later, when it is more advanced.

Billions have been spent on drugs that have proved disappointing or have been discredited. Of the two kinds of Alzheimer’s drugs approved by the FDA — those that may temporarily mitigate certain Alzheimer’s symptoms but have no effect on its progression, and those designed to slow progression — two of the most recent, aducanumab, approved in 2021, and crenezumab, fast-tracked to arrive this year, can have serious side effects, including brain swelling and hemorrhage, with minimal or no benefit. The cost of a year’s worth of aducanumab is $56,000.