A new study reveals that human brains have been getting larger over recent decades. Specifically, people born in the 1970s were found to have brain volumes 6.6% larger and brain surface areas almost 15% larger than those born in the 1930s. This increase in brain size, the researchers suggest, could be boosting our brain reserve, potentially lowering the risk of age-related dementias. The findings have been published in JAMA Neurology.
The overall health of Americans has significantly improved over the past century, despite persisting health disparities. With people living longer, there’s a growing segment of the population at risk for Alzheimer’s disease and related dementias. Interestingly, data, including findings from the renowned Framingham Heart Study (FHS), indicate a decline in dementia incidence.
The researchers were curious if improvements in health, education, and management of vascular risk factors from early life could be leading to better brain development and larger brain sizes.
For their study, the researchers used data from the Framingham Heart Study (FHS), a longitudinal research project initiated in 1948 in Framingham, Massachusetts. This study was designed to explore the patterns and determinants of cardiovascular health, but over the years, it expanded to include investigations into brain health, leveraging the comprehensive data collected across three generations of participants.
The specific subset of data used for this brain study came from high-resolution magnetic resonance imaging (MRI) scans conducted between 1999 and 2019. These scans were from FHS participants born in decades ranging from the 1930s to the 1970s, encompassing a broad spectrum of the population in terms of age and generational health trends.
The total sample for this brain size examination included 3,226 individuals, with a near-even distribution of females and males, all of whom had undergone MRI scans to provide detailed images of their brain structures.
After comparing MRI scans of individuals born in the 1930s to those born in the 1970s, the researchers observed a notable trend: an increase in both brain volume and surface area over this period.
Intracranial volume, representing the total capacity of the skull, increased from an adjusted mean of 1234 mL for individuals born during the 1930s to 1321 mL for those born in the 1970s. On average, individuals born in the 1970s had a cortical surface area of 2,104 square centimeters, in contrast to those born in the 1930s, who had an average area of 2,056 square centimeters.
Similarly, white matter and hippocampal volumes also showed significant increases across birth decades. Interestingly, while brain volume and surface area increased, cortical thickness decreased, suggesting a change in the brain’s architecture over time.
These changes in brain size are not merely reflective of overall body growth trends. Even after adjusting for height and other factors, the increases in brain volume remained significant.
“The decade someone is born appears to impact brain size and potentially long-term brain health,” said Charles DeCarli, first author of the study and a distinguished professor of neurology and director of the UC Davis Alzheimer’s Disease Research Center. “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.”
These findings hint at the possibility of enhanced brain reserve. Brain reserve refers to the brain’s ability to tolerate pathological damage due to aging or disease without manifesting visible symptoms of cognitive decline.
Larger brain volumes and surface areas could potentially offer better protection against age-related diseases, such as dementia and Alzheimer’s disease. This notion is supported by the declining incidence of dementia reported in earlier studies, suggesting that as brains grow larger, they may become more resilient to cognitive impairments.
“Larger brain structures like those observed in our study may reflect improved brain development and improved brain health,” DeCarli said. “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.”
Despite the robust design of the Framingham Heart Study and the careful methodology of this research, the study’s authors caution against overgeneralizing these findings. The predominantly non-Hispanic White, healthy, and well-educated makeup of the study’s cohort may not accurately represent the broader U.S. population.
Moreover, the cross-sectional nature of the study limits causal inferences. Future research could further elucidate these findings through longitudinal studies that track brain changes and cognitive function over time in a more diverse population.
“This study extends current knowledge by showing that secular trends in brain structure are occurring. The larger brain structure, which may reflect improved brain development and brain health, is at least 1 manifestation of improved brain reserve that could buffer the effect of late-life diseases on incident dementia,” the researchers concluded.
The study, titled “Trends in Intracranial and Cerebral Volumes of Framingham Heart Study Participants Born 1930 to 1970,” was authored by Charles DeCarli, Pauline Maillard, Matthew P. Pase, Alexa S. Beiser, Daniel Kojis, Claudia L. Satizabal, Jayandra J. Himali, Hugo J. Aparicio, Evan Fletcher, and Sudha Seshadri.