University of California Davis researchers found a trend in human brain size — they're getting larger. People born in the 1970s had larger brains and more brain surface area than those born in the 1930s.
Does this mean less risk of dementia for younger generations?
Why it matters
Larger brain volume could provide a greater "brain reserve" to help protect against the effects of age-related neurological diseases like Alzheimer's and other dementias.
- With dementia cases expected to surge as the population ages, factors that even moderately lower the risk could have an outsized positive impact.
The big picture
The UC Davis Health researchers analyzed brain scans of over 3,200 participants in the long-running Framingham Heart Study. The participants were born across decades ranging from the 1930s to the 1970s.
- This multi-generational study design gives a rare window into potential secular changes in brain development across 80 birth years.
Key findings
- Steady increases in brain size were found decade-over-decade.
- Those born in the 1970s had:
- 6.6% greater total brain volume
- Nearly 15% larger cortical surface area (the brain's outer folded surface) than those born in the 1930s.
Go deeper
The scientists examined various brain regions and measurements, consistently revealing bigger brains in younger birth decades.
For example, they found the following structures all trended larger:
- White matter
- Gray matter
- The hippocampus (key for learning and memory)
The big idea: Environmental factors like health, social, cultural, and educational influences likely contribute to the observed brain changes over time.
The challenge researchers have is determining the relative impact of external factors and genetics on brain size increase.
The intrigue
Dementia incidence has dropped since the 1970s. For example:
- One study found the incidence rate decreased by 20% per decade since the 1970s.
- The prevalence of dementia among people over age 65 in the US declined from 12.2% in 2000 to 8.5% in 2016, a 3.7 percentage point drop.
- The age-adjusted prevalence of dementia decreased more rapidly between 2000 and 2004 than later years.
Factors contributing to the decline include:
- Increased education levels, especially among men, explained about 40% of the reduction in dementia prevalence for men and 20% for women.
- Improvements in cardiovascular health, including reduced smoking and better management of conditions like high blood pressure, may have also contributed to the decline.
Demographic differences: Most Framingham Heart Study participants are non-Hispanic whites, so the findings may not represent the entire U.S. population.
- The decline in dementia prevalence was more pronounced among men compared to women.
- Racial/ethnic disparities in dementia prevalence narrowed, with a more significant decline seen among Black men compared to White men.
- Dementia prevalence remained higher among racial/ethnic minorities compared to non-Hispanic White individuals.
The takeaway
While the number of dementia cases is expected to grow with an aging population, increasing brain size hints at a potential protective factor that may be helping curb the prevalence of dementia for younger generations.
This is welcome news in the fight against devastating neurological diseases.
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