Humans Brains Are Growing in Size, Possibly Lowering Risk of Dementia

According to the 2023 report by the American Alzheimer's Association, about 6.7 million Americans today over the age of 65 have Alzheimer's disease. This number is expected to double by 2060. Despite the rising cases, the percentage of America's aging population affected by dementia is increasing.

(Photo: Wikimedia Commons/ Hikmet Gümüş)

In a 2016 report by the National Institute of Aging, experts revealed that since the 1970s, the incidence of Alzheimer's in the US has decreased by 20%. Researchers from the University of California Davis may know why.

Increasing Brain Volumes

In a new investigation, a team of researchers led by neurologist Charles DeCarli analyzed brain MRI data from the Framingham Heart Study (FHS). This community-based research has been collecting data since 1948. This study was launched to evaluate patterns in cardiovascular disease and other health issues among the American population.

The new study, "Trends in Intracranial and Cerebral Volumes of Framingham Heart Study Participants Born 1930 to 1970," revealed that human brains are getting more significant. According to DeCarli, the decade someone is born appears to affect brain size and long-term brain health.

The research team used brain MRIs from FHS participants. The original cohort includes 5,209 men and women between 30 and 62. The Framingham Heart Study has continued for 75 years and comprises second—and third-generation participants.

MRIs were conducted between 1999 and 2019 on FHS participants born between the 1930s and 1970s. The brain study consisted of 3,226 participants, with an average age of 57 at the time of the MRI.

Experts from UC Davis compared the MRIs of people born in the 1930s to those born in the 1970s. The analysis discovered gradual but consistent increases in brain structures. For instance, a measure that analyzes brain volume indicates steady increases decade by decade. Participants born in the 1930s had an average brain volume of 1,234 milliliters, while those born in the 1970s had an average volume of 1,321 milliliters, or about a 6.6% increase.

Cortical surface area also showed an even greater increase decade by decade. Participants born in the 1970s had an average surface area of 2,104 square centimeters compared to 2,056 square centimeters for participants born in the 1930s. This indicates almost a 15% increase in volume.

Moreover, brain structures such as the hippocampus, white matter, and gray matter also increased in size when participants born in the 1930s were compared to those born in the 1970s.

Good News for Younger Generations

According to the researchers, larger brains may mean a lower incidence of dementia. DeCarli reported that larger brain structures may reflect improved brain development and enhanced brain health. He further described that a larger brain structure represents a larger brain reserve. This could buffer the late-life effects of age-related diseases such as Alzheimer's and related dementias.

While genetics play a crucial role in determining brain size, the result of the study indicates that external influences may also play a role. By understanding the factors that drive this increase in brain size, the experts hope to gain new insights into the effects of environment and lifestyle factors on our brain health and risk of neurodegenerative disease.