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Human brains are getting larger which could reduce dementia risk, study finds

Breathing woman
Researchers from UC Davis have uncovered a significant trend: human brains are expanding in size across generations. (CREDIT: Creative Commons)

A recent investigation conducted by UC Davis Health researchers has uncovered a significant trend: human brains are expanding in size across generations.

This study, published in JAMA Neurology, reveals that individuals born in the 1970s exhibit brain volumes approximately 6.6% larger and brain surface areas nearly 15% larger compared to those born in the 1930s.


Lead author of the study, Charles DeCarli, a distinguished professor of neurology and director of the UC Davis Alzheimer’s Disease Research Center, suggests that the era of one's birth could influence brain size and potentially long-term brain health. DeCarli emphasizes that while genetics play a crucial role in determining brain size, external factors such as health, social, cultural, and educational influences may also contribute.

Dr. Charles DeCarli
Charles DeCarli is a distinguished professor of neurology and director of the UC Davis Alzheimer’s Disease Research Center. (CREDIT: UC Davis Health)

The research utilized brain magnetic resonance imaging (MRI) data from participants enrolled in the Framingham Heart Study (FHS). Originating in 1948 in Framingham, Massachusetts, the FHS aimed to investigate cardiovascular and other diseases within the community.


The study initially included 5,209 individuals aged 30 to 62, with subsequent generations joining over the 75-year research period.

MRI scans conducted between 1999 and 2019 included participants born from the 1930s to the 1970s. The study encompassed 3,226 individuals, with an average age of approximately 57 at the time of the MRI. Comparing brain MRIs from individuals born in different decades revealed consistent increases in various brain structures over time.


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For instance, intracranial volume, a measure of brain volume, exhibited steady growth from the 1930s to the 1970s cohorts. Participants born in the 1970s showcased an average volume of 1,321 milliliters, a 6.6% increase from the 1930s cohort's average volume of 1,234 milliliters.

Similarly, cortical surface area, indicative of brain surface, demonstrated a notable rise over the decades, with individuals born in the 1970s exhibiting a nearly 15% larger surface area compared to those born in the 1930s.


The study also noted increases in the size of brain structures such as white matter, gray matter, and the hippocampus, which is associated with learning and memory, among individuals born in later decades.

Least-Squares Mean Association (Adjusting for Age and Sex) Between Decade of Birth and Magnetic Resonance Imaging Measures. (CREDIT: JAMA Neurology)

The implications of these findings extend to age-related neurological conditions, particularly dementia. Despite a projected increase in Alzheimer’s cases due to the aging population, there has been a decline in its incidence over the past decades. A previous study reported a 20% reduction in dementia incidence per decade since the 1970s.


DeCarli suggests that improved brain health and size observed in later-born generations may contribute to this decline in dementia incidence. Larger brain structures signify enhanced brain development and health, potentially providing a greater brain reserve that could mitigate the impact of age-related brain diseases like Alzheimer’s and related dementias.

Demographics of Cohort by Decade of Birth. (CREDIT: JAMA Neurology)

The strength of this study lies in the longitudinal design of the FHS, which enables researchers to analyze brain imaging data spanning three generations and nearly 80 years. However, a limitation is the predominantly non-Hispanic white composition of the FHS cohort, which may not fully represent the diversity of the U.S. population.


Additional authors include: Pauline Maillard and Evan Fletcher of UC Davis; Matthew Pase of Monash University, Australia; Alexa Beiser, Daniel Kojis and Hugo Aparicio of Boston University; and Claudia Satizabal, Jayandra Himali and Sudha Seshadri of UT Health San Antonio.

For more science news stories check out our New Discoveries section at The Brighter Side of News.


Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.


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