The risk of developing dementia may be much higher than previously thought, a study published Monday in the journal Nature Medicine has found.
Older studies estimated that about 14% of men and 23% of women would develop dementia in their lifetimes. The new study puts that estimate higher, at around 42% for both men and women.
“I think this is going to be a very important study, and I think it is going to change the way we look at dementia,” said Dr. Ted Huey, director of the memory and aging program at Butler Hospital in Rhode Island, who wasn’t involved with the research.
More than anything, the increase in both risk and the number of people living with dementia — which the researchers estimated will double by 2060 — is the result of people living longer than previous generations, said study leader Dr. Josef Coresh, director of the Optimal Aging Institute at the NYU Grossman School of Medicine.
“Just the fact that the population is going to get older will mean the number of dementia cases will double overall,” Coresh said. Among Black Americans, for whom the risk is greater, the number of cases is expected to triple, he said.
About 10% Americans over age 65 have been diagnosed with dementia, according to the Centers for Disease Control and Prevention.
The study included more than 15,000 people in the U.S. who were tracked for more than two decades. About one-quarter of the participants were Black and more than half were women — two groups known to have elevated risk.
According to the study, the average 55-year-old’s risk of dementia during their lifetime is 42%, but the risk was not the same at every age. The brunt of it occurred after a person’s 85th birthday. Between ages 55 and 75, the average person’s risk of developing dementia was 4%, according to the study. By the time someone turned 85, their risk was about 20%. Risk didn’t reach 42% until a person’s 95th birthday.
For Black Americans and women, the risk was higher, but the pattern was similar.
Black Americans had a 7% risk by age 75, nearly double the average. By 85, the risk jumped to 28%, and by 95 it was 42%. For women, this risk was 3% by 75, 21% by 85 and 48% by age 95.
“We need to think about the causes for this risk and how to prevent it,” Coresh said.
Past research has found elevated risk may be caused by higher rates of diabetes and hypertension in Black Americans, largely due to inequalities regarding access to care, and structural racism that can cause stress, which puts people at higher risk for dementia.
A lot of the elevated risk found in women can be attributed to the fact that, on average, women live longer than men — but that isn’t the whole story. A genetic variant called APOE-4, which elevates a person’s risk for Alzheimer’s disease, the most common type of dementia, may raise risk more for women than for men in certain age groups. Research into whether pregnancy has any part in dementia risk has produced mixed results.
Why is dementia risk higher than before?
Prior studies suggested that about 14% of men and 23% of women would develop dementia in their lifetimes. The 42% risk these researchers found is much higher, which may be explained by several factors, experts said.
Previous studies, including the Framingham Heart Study and the Rotterdam Study, both published in the late 1990s, included a less diverse group of participants, all of whom lived in the same city. It’s an issue, experts say, that’s pervasive in dementia research.
Dr. Monica Parker, an associate professor of neurology at Emory University’s Goizueta Alzheimer’s Disease Research Center, sees patients as a primary care provider at Good Samaritan Health Clinic in Atlanta. Many of her patients are immigrants and do not speak English.
“Most of our academic health centers aren’t set up to see non-English-speaking people,” meaning this section of the population is often left out of the research, said Parker, who is also the chair of the Alzheimer’s Foundation of America’s medical, scientific and memory-screening advisory board and has been a paid educational consultant for Eli Lilly, Biogen and Eisai, three companies that make Alzheimer’s drugs.
Other studies may have struggled to keep in touch with participants who developed dementia, said Huey.
The researchers in this study, however, “did a very good job of following people,” he said.
Finally, a lot of dementia data that exists singles out just one type: Alzheimer’s disease.
“Saying dementia is like saying cancer. You have a lot of subtypes,” said Michelle Mielke, a professor and the chair of epidemiology and prevention at the Wake Forest University School of Medicine in North Carolina.
Alzheimer’s disease is the most common type of dementia, accounting for as much as 80% of cases, according to CDC data. Research that only tracks Alzheimer’s, however, leaves out dementia caused by other conditions such as cardiovascular and neurological disease, Mielke said.
“All aging-related diseases are increasing with this aging population, we are seeing increases in stroke, and that is going to be a risk factor for vascular dementia,” she said. “Sometimes we are a victim of our own success. People are living longer with a lot more comorbidities.”
Those comorbidities, including stroke, high blood pressure and Type 2 diabetes, all increase a person’s risk for dementia. It’s also likely more cases that would have previously gone unrecognized are being diagnosed, said Dr. Peter Whitehouse, a professor of neurology at Case Western Reserve University in Ohio.
In 2011, under the Affordable Care Act, Medicare began reimbursing providers for annual wellness visits that include screening for cognitive decline.
“If more people are coming into a physician’s office, they may be screening more, and more cases will show up,” Whitehouse said.
Although the new data is stark compared to previous numbers, Dr. Andrea Bozoki, division chief of cognitive and behavioral neurology at the University of North Carolina School of Medicine, said people should remember that not everyone will develop dementia in old age.
“Less than half of people who make it to age 95 will have dementia,” she said. “Dementia is not an inevitable part of aging, no matter how old you are.”
While certain factors that increase dementia risk, such as genetics or exposure to air pollution, may be out of a person’s control, the good news is there are plenty of ways to lower dementia risk.
“Making sure hypertension and diabetes are controlled certainly will help with cognition,” Mielke, of Wake Forest University, said.
Getting quality sleep, which includes treating issues such as sleep apnea, can also lower dementia risk, as can eating a healthy diet. As a rule of thumb, what’s good for the heart is also good for the brain, and vice versa.
“We know that the vascular risk factor modifications that help your heart also help your brian,” Coresh said.
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