Newer Generations with Larger Brains are Influencing Dementia
Larger brain size indicates enhanced brain health and cognitive abilities. Since the 1930s, there has been a consistent increase in brain size. A recent study highlights the implications of this growth on the likelihood of developing dementia, specifically Alzheimer’s disease.
By 2020, more than 55 million people worldwide had dementia, with projections indicating a doubling of this figure every two decades.
This rise is largely due to the aging population and longer lifespans. A 2016 study funded by the National Institutes of Health (NIH) found a consistent decrease in newly reported dementia cases since the 1970s, with an average decline of 20% per decade.
However, what factors are behind this decline? The 2016 study investigated the influence of education, among other variables, on the risk of dementia.
Education and Dementia Incidence
It revealed that by the 2000s, there was a 44% decrease in incidence among individuals with at least a high school diploma compared to the 1970s. While acknowledging the correlation between education and dementia, the study did not explore the potential cause(s) behind this trend.
A recent study conducted by UC Davis Health might shed light on this issue: It suggests that our brains have simply grown larger over time.
“The decade of someone’s birth seems to have an impact on brain size and potentially influences long-term brain health,” explained Charles De Carli, a professor of neurology and the director of the UC Davis Alzheimer’s Disease Research Center, who led the study.
“While genetics plays a significant role in determining brain size, our findings suggest that external factors such as health, social, cultural, and educational influences may also contribute.”
Researchers at UC Davis utilized the same dataset as the previous study, drawing from the Framingham Heart Study (FHS). This ongoing community-based study, initiated in 1948, involves over 15,000 individuals from Framingham, Massachusetts, spanning three generations, aimed at tracking heart and brain health trends.
Between 1999 and 2019, brain MRIs were conducted on FHS participants, and the researchers analyzed scans from 3,226 individuals (53% female, 47% male) born between 1930 and 1970.
None of the participants exhibited cognitive impairment or had a history of stroke, factors known to increase the risk of dementia.
Brain Evolution Across Decades
When comparing the MRIs of individuals from the 1930s to those born in the 1970s, the researchers observed gradual yet consistent enlargements in several brain structures.
Notably, intracranial volume (ICV), representing the volume within the skull, increased steadily from an average of 1,234 mL/41.7 fl oz in the 1930s to 1,321 mL/44.7 fl oz in the 1970s—a 6.6% rise per decade.
Despite the fact that individuals were taller in the 1970s compared to the 1930s, adjustments for height did not eliminate the differences in ICV. Previous studies have suggested that a larger ICV signifies a greater ‘brain reserve,’ potentially offering protection against dementia.
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Brain Structure Expansion
The study revealed growth in both white matter and cortical gray matter volumes. Gray matter, essential for mental functions, memory, emotions, and movement, forms the brain’s outer surface, known as the cortex.
Conditions like stroke, Parkinson’s disease, and Alzheimer’s can impact gray matter. White matter, situated beneath gray matter, consists of nerve fiber bundles coated with myelin, providing electrical insulation and its characteristic white appearance. Over the span from the 1930s to the 1970s, white matter volume increased by 7.7%, while cortical gray matter volume rose by 2.2%.
Furthermore, the hippocampus volume, responsible for short-term memory and its transfer to long-term storage, saw a 5.7% increase. The cortical surface area, the visible wrinkled layer of gray matter, expanded by 14.9%.
DeCarli noted, “Larger brain structures like those observed in our study may indicate enhanced brain development and improved brain health. A larger brain reserve could potentially mitigate the effects of age-related brain diseases like Alzheimer’s and related dementias in later life.”
Early-Life Environment and Brain Structure
The researchers, while acknowledging genetics’ significant role, suggest that early-life environmental factors likely contribute more to larger brain structures and reduced dementia risk.
They propose that the observed increase in brain size reflects advancements in health, education, and sociocultural factors since the 1930s, along with improvements in modifiable dementia risk factors such as heart disease, high blood pressure, obesity, exercise, and diabetes.
Yet, a constraint of the research lies in the fact that the FHS group primarily consists of non-Hispanic White individuals who are in good health and possess higher levels of education.
Consequently, it lacks representation from the wider U.S. populace. However, the study’s strength lies in its design, which tracked a substantial number of participants across a significant portion of their lives, spanning nearly 80 years of birth cohorts.
Read the original article on: New Atlas
