Dementia Risk May Fall as Younger Generations Have Larger Brains

Human brains are getting bigger, which might spell good news for our overall brain health.

Alzheimer’s disease affects roughly 6.7 million Americans today over the age of 65, according to a 2023 report by the American Alzheimer’s Association. Barring the discovery of medical breakthroughs in Alzheimer’s treatment, this number is expected to double by 2060.

But despite the absolute numbers of Alzheimer’s cases rising, in line with America’s aging population, the percentage of the population affected by the dementia disease is actually decreasing.

In a 2016 report by the National Institute of Aging, researchers found that, since the 1970s, Alzheimer’s incidence in the United States has actually decreased by 20 percent. And now, researchers from UC Davis Health may know why.

In a new study published in the journal JAMA Neurology, the team led by neurologist Charles DeCarli analyzed brain MRI data from a community-based study that has been collecting data since 1948 called the Framingham Heart Study. The study was launched to assess patterns in cardiovascular disease and other health issues among the American population, and as part of their long-term analysis, MRI scans were conducted between 1999 and 2019 on participants born between the 1930s and 1970s.

In total, 3,226 participants received MRIs.

By comparing scans from those born in the 1930s to those born in the 1970s, the team saw a gradual but consistent increase in several brain structures. For example, participants born in the 1970s showed a 6.6 percent greater brain volume on average and a 15 percent increase in surface area.

“Larger brain structures like those observed in our study may reflect improved brain development and improved brain health,” DeCarli said in a statement. “A larger brain structure represents a larger brain reserve and may buffer the late-life effects of age-related brain diseases like Alzheimer’s and related dementias.”

The study is not without limitations—for example, participants were predominantly non-Hispanic white and therefore not representative of the broader U.S. population—but identifying these trends could have important implications for population brain health in the future.

The reason for the apparent increase in brain size is unclear, but DeCarli believes it to be a combination of internal and external factors.

“Genetics plays a major role in determining brain size, but our findings indicate external influences — such as health, social, cultural and educational factors — may also play a role,” he said.

By understanding the factors driving this increase in brain size, the researchers hope to gain new insights into how our environment and lifestyle factors can influence our brain health and risk of neurodegenerative disease.

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