Gaby
Evidence shows the human brain has been getting larger since the 1930s. Studies link larger brain size with better health and stronger cognitive function. Researchers at the University of California, Davis, investigated how that trend affects the risk of developing dementia.
A Brief History of the Issue
In 2020, over 55 million people worldwide were living with dementia. Experts warned the number could double every 20 years. Still, the rising prevalence likely reflects the aging global population and increased longevity. A 2016 National Institutes of Health study found a gradual decline in new dementia cases since the 1970s, averaging about a 20 percent decrease per decade.
But what contributes to that decline? Among other factors, researchers examined the impact of education on dementia risk. They found that, compared with people in the 1970s, the incidence of dementia had decreased by 44 percent among individuals who had at least a high school education by around 2000. While the study linked education and lower dementia rates, it didn’t pin down the underlying causes.
Insights from the Authors of the New Study
“Genetics play a significant role in determining brain size, but our findings suggest that external factors, such as health, social, cultural, and educational influences, may also play a part,” said Charles DeCarli, a professor of neurology, director of the Alzheimer’s Disease Research Center at the University of California, Davis, and the lead author of the study.
His team used the same dataset analyzed in earlier work—the Framingham Heart Study (FHS). Launched in 1948, that long-running study included more than 15,000 participants from Framingham, Massachusetts, across three generations. The goal was to identify trends in brain and heart health, as reported by New Atlas.
From 1999 to 2019, researchers examined MRI scans of 3,226 people (53% women, 47% men). All participants were born between 1930 and 1970, and none had a history of cognitive impairment or stroke, both of which increase dementia risk.
When researchers compared scans of people born in the 1930s with those born in the 1970s, they saw a gradual but consistent increase in the size of certain brain structures. For example, intracranial volume (ICV) rose from an average of 1,234 ml (41.7 fluid ounces) in those born in the 1930s to 1,321 ml (44.7 fluid ounces) in those born in the 1970s—a 6.6 percent increase.
Across generations, white matter volume increased by 7.7 percent and cortical gray matter volume by 2.2 percent. The hippocampus, which helps form new memories and consolidate them into long-term storage, grew by 5.7 percent. The cortical surface area—the wrinkled outer layer of gray matter—expanded by 14.9 percent.
DeCarli says the increases in these brain structures may reflect improved brain development and health. A larger brain can provide greater reserve, which may help lessen the impact of age-related conditions such as Alzheimer’s disease and other dementias.
Researchers acknowledge that genetics remain a major factor in cognitive health. Still, they argue that early-life environmental factors likely contributed to larger brain structures and the fall in dementia risk. The trend probably reflects improvements in health, education, and sociocultural conditions since the 1930s.
The study’s findings were published in JAMA Neurology.
