The Growing Size of Human Brains May Have An Effect on Long-term Brain Health

According to a recent study, human brain size has increased recently. In particular, it was discovered that compared to those born in the 1930s, individuals born in the 1970s had brain volumes that were 6.6% larger and brain surface areas that were over 15% larger. The researchers hypothesize that this increase in brain size may be increasing our brain reserve and so reducing the likelihood of dementias associated with aging.

Despite ongoing health disparities, Americans’ general state of health has greatly improved over the previous century. An increasing proportion of the population is at risk for Alzheimer’s disease and other dementias as a result of longer lifespans. It’s interesting to note that data show a drop in the incidence of dementia, including those from the famed Framingham Heart Study (FHS).

The researchers wanted to know if larger brain sizes and better brain development could be caused by early life improvements in vascular risk factor management, education, and health.

The Framingham Heart Study (FHS), a longitudinal research project started in 1948 in Framingham, Massachusetts, provided the researchers with data for their investigation. Initially intended to investigate patterns and factors of cardiovascular health, this project has since broadened to include inquiries into brain health by utilizing the extensive data gathered from participants spanning three generations.

A particular subset of data from high-resolution magnetic resonance imaging (MRI) scans performed between 1999 and 2019 was utilized in this brain study. The FHS participants whose scans were included in this study were born between the years of the 1930s and the 1970s, representing a wide range of ages and health patterns across generations.

3,226 people in all, nearly evenly split between males and females, made up the sample for this investigation of brain size. Each person had received an MRI scan to obtain precise photographs of their brain anatomy.

The researchers noticed a noteworthy trend in the MRI scans of people born in the 1930s and 1970s: a rise in both brain volume and surface area over this time.

The overall capacity of the skull, or intracranial volume, rose from an adjusted mean of 1234 mL for those born in the 1930s to 1321 mL for people born in the 1970s. The cortical surface area of people born in the 1970s was 2,104 square centimeters on average, but the average area of people born in the 1930s was 2,056 square centimeters.

In a similar vein, large increases in white matter and hippocampus sizes were observed across birth decades. It’s interesting to note that cortical thickness dropped as brain volume and surface area rose, indicating a shift in the architecture of the brain over time.

These variations in brain size are not only a reflection of general patterns in bodily growth. Once height and other variables were taken into account, the gains in brain volume persisted.

Charles DeCarli, a distinguished professor of neurology and the director of the UC Davis Alzheimer’s Disease Research Center, remarked of the study’s first author, Charles DeCarli, that “the decade someone is born appears to impact brain size and potentially long-term brain health.” “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 results suggest that brain reserve may be improved. The term “brain reserve” describes the brain’s capacity to withstand pathological damage brought on by aging or illness without exhibiting overt signs of cognitive impairment.

Greater defense against age-related illnesses like dementia and Alzheimer’s disease may be provided by larger brain volumes and surfaces. The decreasing incidence of dementia found in previous studies lends credence to the idea that larger brains may be more resistant 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.”

The researchers advise against drawing undue conclusions from this study, even with the strong design of the Framingham Heart Study and the meticulous technique used. The research group may not be a true representation of the larger American community due to its predominately non-Hispanic White, healthy, and well-educated demographics.

Furthermore, conclusions on causality are limited by the study’s cross-sectional design. Through longitudinal studies that monitor changes in the brain and cognitive performance over time in a more diverse population, future research may be able to clarify these findings even more.

“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.