What Middle-Aged People Can Do Now to Help Prevent Dementia Later

The fight against dementia actually starts in your 40s.

Midlife, not your 70s or 80s, is when brain changes start to occur that can pave the way toward dementia, Alzheimer’s disease and cognitive decline later, according to a growing body of research. 

Intervening earlier to improve brain health—and studying the midlife brain more closely—might help people stay sharper in their later years, researchers say. Regular exercise, getting enough sleep and doing activities that keep your brain stimulated are all steps that can help you combat dementia later in life.

“Middle age is an opportune time to make lifestyle choices and obtain treatment that will bring an enormous return on investment in old age,” says Terrie Moffitt, a professor of psychology and neuroscience at Duke University.

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More scientists are looking for clues in the midlife brain because efforts to target dementia in older people have largely failed, says Ahmad Hariri, a professor of psychology and neuroscience also at Duke.

Nearly seven million Americans have Alzheimer’s disease, the most common type of dementia, according to the Alzheimer’s Association. The figure is expected to rise to nearly 13 million by 2050.

“A very reasonable interpretation of those failures is that interventions were attempted too late after too much damage had accrued in the brains,” Hariri says. 

What happens to the brain in midlife

As the number of people projected to get dementia increases, many of us are worried about our risks later in life. Doctors and scientists are closely focusing on it too. 

Parts of the brain start to change faster during middle age, especially the hippocampus, which is important for remembering everyday events, says Sebastian Dohm-Hansen, a doctoral student at University College Cork in Ireland and first author of a March review study on brain aging published in the journal Trends in Neurosciences.

In your 40s and 50s, the white matter in your brain—the connections between brain areas—decreases in volume, says Dohm-Hansen. That likely results in slower processing speed, which could have further effects on cognition, he says.

In addition, proteins can build up in your blood, resulting in low-grade inflammation that can affect the hippocampus’s ability to encode and store new information, he says. 

People keep their verbal language-based skills their whole life, says Moffitt. But the speed at which you process information and your capacity to solve new problems of logic and reasoning gradually diminishes with age. 

Her research has found that certain groups of people lose cognitive function faster during midlife. That includes people who began using cannabis or tobacco as teenagers and continued to use in their 40s, and people with high levels of toxic lead in their blood from childhood. But even outside of those groups, some people are aging faster in their 40s and 50s, which research has suggested can be linked with developing dementia later in life.

Women in midlife are grappling with the added complications of the menopause transition, during which abrupt changes in hormone levels can affect the brain, says Jessica Caldwell, director of the Cleveland Clinic’s Women’s Alzheimer’s Movement Prevention Center in Las Vegas. A woman’s brain can adapt to these changes by reorganizing itself, but scientists are still studying how that happens and what the ultimate impact is.

Not everyone believes midlife is a sharp turning point in brain health. Processing speed is the cognitive function that declines most as people age, but that slide happens gradually and varies from person to person, says Dr. David Knopman, a professor of neurology at Mayo Clinic in Rochester, Minn.

OK, so what can you do?

Keeping your heart healthy in midlife is the best way to stave off cognitive decline, says Knopman. Brain and heart health are closely connected. 

The same things that can lead to a blockage of arteries to the heart can affect arteries to the brain, impeding blood flow and oxygen delivery.  

There are no guaranteed ways to prevent dementia. But steps that help both your brain and your heart include exercising regularly, eating a healthy diet, and not smoking, as well as trying to avoid getting or managing conditions such as diabetes, high blood pressure and cholesterol, and obesity, and treating obstructive sleep apnea.

For middle-aged patients, doctors often focus on emphasizing lifestyle changes such as diet and exercise to manage blood pressure and diabetes risk, says Caldwell. But those steps are equally important for brain health down the line. 

“Eating a more nutritious diet, getting exercise, and sleeping sufficiently are all associated with better brain health outcomes,” says Caldwell. 

Also important is staying socially and mentally active and engaged, Knopman says. “There are benefits of working in a challenging environment—it stimulates the brain—and it seems to be associated with better outcomes,” he says.

There’s no reason to wait till midlife to start making these health improvements, either, notes Kristine Beate Walhovd, a psychology researcher in the Center for Lifespan Changes in Brain and Cognition at the University of Oslo in Norway. Many of the lifestyle changes that will set you on a better path in old age can begin before midlife, she notes.

Write to Sumathi Reddy at Sumathi.Reddy@wsj.com