The average human brain has been growing over the last century, according to research.
- Dementia is a growing problem worldwide, with
numbers predicted to almost triple over the next 30 years.
- The rise is generally attributed to the growing
and aging population, but lifestyle can also contribute.
- However, a new study suggests there may be some
good news in the field of dementia.
- It found that people’s brains have been getting
larger over the past 100 years, and this increased brain reserve could,
potentially, reduce the risk of age-related dementias.
As healthy people get older, the brain
A new study, from UC Davis Health, has suggested that
it might. Researchers found that people born in the 1970s had brains that were,
on average, 6.6% larger than those of people born in the 1930s. They suggest
that larger brain size means increased brain reserve — which may reduce the
risk of age-related dementias.
The study is published in
“While these newly
published results add to the body of literature on brain size and changes over
time, this study was largely conducted in healthy, well-educated, non-Hispanic
White individuals, and so [these findings] are not necessarily generalizable to
other groups or individuals.”— Ozama Ismail, PhD, Alzheimer’s Association
director of scientific programs, who was not involved in the study.
Dementia’s
effects on the brain
Currently,
Although some memory loss is a natural part of aging,
dementia is not. Dementia describes a range of diseases, with the most common,
being Alzheimer’s
disease, causing 60-80% of cases. Others include vascular dementia, Lewy body dementia (which
may be associated with Parkinson’s disease), frontotemporal dementia, and mixed dementia.
Symptoms of dementia, which worsen over time,
may include:
- memory
problems
- asking
the same question repeatedly
- difficulty
finding or understanding words
- feeling
confused in unfamiliar environments
- problems
dealing with money and numbers
- anxiety
and withdrawal
- difficulty
planning and carrying out tasks
- mood,
personality and behavior changes
- sleep
disturbances
- obsessive
tendencies
In all types of dementia,
as brain cells are damaged and die, there is some degree of
Human brain
sizes are increasing
This study looked at
participants in the Framingham Heart Study (FHS).
This long-term study has followed 15,000 individuals for more than 75 years.
Of the FHS cohort, 3,226 people had two MRI scans that
were suitable for this study. Of them, 1,706 (53%) were women, and 1,520 (47%)
were men. The scans measured intracranial volume (ICV), cortical gray matter,
cerebral white matter, hippocampal volume, cortical surface area, and cortical
thickness measures.
The participants were all born between 1930 and 1970,
with the median decade of birth being the 1950s. People born in the 1970s were,
on average, 1.6 inches taller than those born in the 1930s, so the researchers
adjusted for this when comparing brain measurements.
People
born in the 1970s had greater brain volumes than those born in the 1930s.
They had a 6.6% greater ICV, 7.7% more white matter,
2.2% more cortical gray matter, 5.7% greater hippocampal volume, and 14.9%
larger cortical surface area. The one measure that had decreased was cortical
thickness, which was 20.9% lower. These differences remained significant when
the researchers adjusted for height differences.
“The decade someone is born appears to impact brain
size and potentially long-term brain health,” said Charles DeCarli, MD, first author of the study,
distinguished professor of neurology, and director of the UC Davis
Alzheimer’s Disease Research Center in a press release.
“Genetics plays a major role in determining brain
size, but our findings indicate external influences — such as health, social,
cultural and educational factors — may also play a role,” he said.
“Larger brain structures
like those observed in our study may reflect improved brain development and
improved brain health. 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.”— Charles DeCarli, MD
Larger brain
size may indicate lower dementia risk
Previous
studies have
suggested that larger brain volume protects against the effects of dementia
pathology, arguing that those with a greater head circumference can endure a
greater degree of damage before they start to show cognitive impairment.
This
However, this observed effect could be due to other
factors, as Ismail told Medical News Today:
“Larger brain volumes may
be beneficial in maintaining resilience to cognitive decline and dementia, but
many other factors can contribute to resilience, including genetics,
environment, socioeconomic status, education, and active vs. sedentary
lifestyle.”
The researchers in this study suggest that the
increase in brain volumes over the four birth decades in their study could
predict a lower risk of dementia in people born later in the FHS.
Call for
more diverse studies
The researchers acknowledge
that their study cohort was predominantly non-Hispanic White, healthy, and
well-educated, so not representative of the general population of the United
States. However, they emphasize that the strengths of the study include the
fact that it has followed 3 generations, spanning more than 80 years of births.
Ismail called for further studies that include a
greater diversity of people:
“More diversity in research
populations is needed before conclusions can be made about changes in brain
size over generations and the influence it may have on cognition, resilience,
and dementia risk.”
“This is particularly important given the known
sociocultural and health disparities that exist in underrepresented
populations,” he added.
The Alzheimer’s Association’s U.S. Study to Protect
Brain Health Through Lifestyle Intervention to Reduce Risk (U.S. POINTER),
which should publish results next year, aims to help address this gap in the
research, as Ismail told MNT:
“In the U.S. POINTER Study, more than 2,000 volunteer
older adults who are at increased risk for cognitive decline are enrolled and
will be followed for two years. Nearly 30% of current participants are from
populations historically underrepresented in Alzheimer’s/dementia research.”
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