“Bigger is always better” may not apply to everything in life, but new research shows the idiom holds true for humans’ brains. Scientists at the University of California have found that human brain size has steadily increased for people born after the 1930s—and this increase in size potentially reduces the overall risk of age-related dementias.
The study is unique in that the sample spans 75 years, now including second and third generations of the original participants who signed on to the Framingham (Mass.) Heart Study in 1948. The original cohort comprised 5,209 men and women between the ages of 30 and 62, with the initial goal to analyze patterns of cardiovascular and other diseases.
Now, University of California, Davis has used the data from the unique pool of participants to draw conclusions on brain health.
For the study, published in JAMA Neurology, the UC Davis team compared MRIs taken between 1999 and 2019 of participants born during the 1930s through the 1970s. This sub-sample comprised 3,226 people (53% female, 47% male) with an average age of about 57 at the time of the MRI.
The results showed gradual but consistent increases in several brain structures. For example, participants born in the 1930s had an average intracranial volume of 1,234 mL, compared with those born in the 1970s who had an average volume of 1,321 mL—about 7% greater.
Cortical surface area—or a measure of the brain’s surface—showed an even greater increase decade by decade. Participants born in the 1970s had an average surface area of 2,104 square centimeters compared with 2,056 square centimeters for participants born in the 1930s—almost a 15% increase in volume.
Importantly, the researchers found brain structures such as white matter, gray matter and the memory-holding hippocampus also increased in size when comparing participants born in the 1930s with those born in the 1970s.
“Larger brain structures like those observed in our study may reflect improved brain development and improved brain health,” said first author Charles DeCarli, director of the UC Davis Alzheimer’s Disease Research Center. “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.”
According to the Alzheimer’s Association, approximately 7 million Americans are currently living with Alzheimer’s disease. That number is expected to rise to 11.2 million by 2040—but, the number is rising in response to America’s aging population. The incidence of Alzheimer’s—or the percentage of the population affected by the disease—is actually decreasing. A previous study found a 20 percent reduction in the incidence of dementia per decade since the 1970s.
Improved brain size could be one reason why.