(CNN) — One in 10 Americans over 65 had dementia, while 22 percent experienced mild cognitive impairment, the earliest stage of the slow slide into senility, according to a new study conducted between 2016 and 2017.

The research, which the authors said is the first nationally representative examination of cognitive impairment prevalence in more than 20 years, was able to measure prevalence of dementia and mild cognitive impairment by age, education, ethnicity, gender and race.

The results showed older adults who self-identified as Black or African American were more likely to have dementia, while those who identify as Hispanic were more likely to suffer from mild cognitive impairment. People who had less than a high school education were more likely to have both conditions.

"Dementia research in general has largely focused on college-educated people who are racialized as white," lead study author Jennifer Manly said in a statement.

"This study is representative of the population of older adults and includes groups that have been historically excluded from dementia research but are at higher risk of developing cognitive impairment because of structural racism and income inequality," said Manly, professor of neuropsychology at the Gertrude H. Sergievsky Center and the Taub Institute for Research on Alzheimer's Disease and the Aging Brain at Columbia University.

"If we're interested in increasing brain health equity in later life, we need to know where we stand now and where to direct our resources," Manly said.

In-Depth Analysis

The study, published Monday in the journal JAMA Neurology, analyzed data from in-depth neuropsychological tests and interviews with nearly 3,500 people over age 65 enrolled in the Health and Retirement Study, a long-term research project sponsored by the National Institute on Aging and the Social Security Administration.

The research was based on a randomly selected sample of people from the study that completed the core survey and underwent neurological testing between June 2016 and October 2017.

Fifteen percent of people who identified as Black tested positive for dementia, while 22 percent had mild cognitive decline, the study found. Ten percent of people who identified as Hispanic had dementia, but the rate of milder issues was higher — 28 percent tested positive for mild cognitive impairment. Nine percent of White people had dementia, while 21 percent had mild cognitive impairment.

Educational achievement, which experts consider to be protective against cognitive decline, showed a significant divide: Nine percent of people with a college degree tested positive for dementia, compared with 13 percent of those who never received a high school diploma. Twenty-one percent of people over 65 with college degrees had mild cognitive decline, compared with 30 percent of those with less than a high school degree.

The extreme elderly had the highest rates of dementia and mild cognitive impairment. Only 3 percent of adults between 65 and 69 tested positive for dementia, compared with 35 percent of those 90 and older.

In fact, every five-year increase in age was associated with higher risk of dementia and mild cognitive impairment, the report said. The study, however, found no differences between men and women in rates of either condition

Mild Dognition Symptoms

Symptoms of mild cognitive impairment can include losing items, forgetting to do things or go to appointments, or struggling to come up with words. A loss of smell and taste and movement issues can also be symptoms, according to the National Institute on Aging.

People with mild cognitive impairment are fully capable of taking care of themselves, "but what they have to go through to do so is exhausting," Laura Baker, a professor of gerontology and geriatric medicine at Wake Forest University School of Medicine in Winston-Salem, North Carolina, told CNN in an earlier interview. She was not involved in the current study.

People with mild cognitive impairment may not remember where they are supposed to be, Baker said. " 'Let me check my calendar. Oh, I forgot to write on this calendar. Let's check another calendar. Oh, I can't find that calendar. I've lost my phone. Where is the key? I can't find the key.' They're able to regroup in the early stages and accomplish things, but the toll is immense."

Not everyone with mild cognitive impairment goes on to develop dementia, although many do, experts say. Lifestyle changes may be a key to reversing mental decline. A 2019 study found personalized lifestyle interventions -— such as diet, exercise, stress reduction and sleep hygiene — not only stopped cognitive decline in people at risk for Alzheimer's, but actually increased their memory and thinking skills over 18 months. Women responded better than men, a follow-up study found.

A February study found about a third of women 75 years or older with mild cognitive impairment reversed their progression to dementia at some point during follow-up. All of the women, however, had high levels of education and academic performance and excellent written language skills, or what experts call "cognitive reserve."

Symptoms of Dementia

Signs of dementia can differ from one person to the next, and can include memory loss and confusion, difficulty speaking, understanding and expressing thoughts, or reading and writing, according to the National Institutes of Health.

People with dementia can act impulsively or show poor judgment, and they can have trouble paying bills or handling money responsibly. They may repeat questions, use strange words to refer to familiar objects and take longer than usual to complete daily tasks.

Wandering and getting lost in a familiar neighborhood is another sign of dementia, as is losing interest in daily activities or events or acting as if they don't care about other people's feelings. They may lose their balance or have other problems with movement. At times, people with dementia can hallucinate or experience delusions or paranoia.

Alzheimer's disease is the most well-known cause of dementia, but cognitive issues can be caused by vascular problems that block the flow of blood to the brain or via ministrokes caused by tiny blood clots traveling to the brain. Frontal lobe dementia, a rare form thought to be associated with abnormal amounts of the proteins tau and TDP-43, often begins in people younger than 60. Another type of decline, called Lewy body dementia, is thought to be caused by abnormal deposits of the protein alpha-synuclein, which are called Lewy bodies.

A person with signs of cognitive decline or dementia needs a full workup by a neurologist to determine the underlying cause, the NIH said. Side effects from a number of medications can mimic dementia, as can certain diseases, such as Huntington's disease.

If you've just been diagnosed with dementia, continue to meet with doctors and specialists and consider asking for a referral to a memory clinic, according to the National Institutes of Health. Reach out to your local Alzheimer's Disease Research Center and consider joining a clinical trial.

The Alzheimer's Association has detailed information on the differences between dementia and Alzheimer's, and it offers many levels of support for both patients and caregivers.

Work on staying healthy — exercise helps with mood, balance and thinking, while eating a well-balanced diet and getting quality sleep can improve the brain's ability to function.

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