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eing overweight can lead to several
health problems. Scientists now believe that obesity in the stomach area could
even have associations with a smaller brain size.
A
new study investigated the links between obesity and brain size.
Researchers
already know that the size of the brain can determine its health and function.
However,
they know much less about what affects brain size itself.
According
to Mark Hamer, a professor at Loughborough University in the United Kingdom:
"Existing
research has linked brain shrinkage to memory decline and a higher risk
of dementia, but research on
whether extra body fat is protective or detrimental to brain size has been
inconclusive."
Prof.
Hamer is one of the authors of a new study focusing on the impact of body fat
on brain size.
Published in the journal Neurology, the study used a particularly large sample size in
comparison with others on the same topic.
In
total, 9,652 people involved in the UK Biobank — which is a database that tracks the health
of around 500,000 people — agreed to take part. Participants were aged 55, on
average.
Taking accurate measurements
In
order to determine body fat figures, the scientists worked out the body mass
index (BMI), waist-to-hip ratio, and overall body fat
of each participant.
Doctors
can calculate BMI by dividing a person's weight by the square of their height.
Dividing waist circumference by hip circumference provides waist-to-hip ratio.
The higher the ratio, the larger a person's stomach compared with their hips.
Specialists
consider people with a BMI of 30 and over to have obesity. Central obesity — or obesity
around the stomach area — is a little different. In this case, a man with a
waist-to-hip ratio above 0.90 and a woman with one above 0.85 is considered to
have central obesity.
The
team calculated brain size using MRI scans and examined the volumes of
both white and gray brain matter. Both of these are important in different
ways.
In
gray matter, the majority of the brain's 100 billion nerve cells are contained.
It also houses parts that deal with muscle control and sensory perception.
White matter, on the other hand, is full of bundles of nerve fibers that
connect parts of the brain.
Before
coming to any conclusions, the scientists took into account a number of things
that affect brain volume — including age, high blood pressure,
levels of physical activity, and whether a person smokes.
Gray matter changes
Their
results indicated several links between body fat and brain size. People who had
both a higher BMI and waist-to-hip ratio had the lowest brain volume overall.
Those who just had a high BMI had slightly lower brain volumes than those who
did not.
Also, 1,291 people with both a high BMI and a high
waist-to-hip ratio had the lowest gray matter brain volume. On average, this
equated to 786 cubic centimeters.
In
contrast, 3,025 people of a healthy weight had 798 cubic centimeters of gray
matter. Lastly, 514 people who had a high BMI but a healthy waist-to-hip ratio
had an average gray matter volume of 793 cubic centimeters.
The
researchers saw no notable differences in white matter brain volume, but they
did find a link between being overweight and a decrease in size in regions of
the brain associated with motivation and reward.
Cause and effect
Prof.
Hamer and his colleagues explain that "obesity, specifically around the
middle, may be linked with brain shrinkage."
However,
they could not determine whether obesity results in changes in brain volume, or
whether "abnormalities in brain structure lead to obesity."
The
study authors did say that only 5 percent of people invited to take part
consented to doing so, and that those who agreed were, on average, healthier
than those who did not.
Therefore,
it is difficult to say whether these results would be applicable to the general
population.
"This
will need further research but it may be possible that someday regularly
measuring BMI and waist-to-hip ratio may help determine brain health,"
Prof. Hamer concludes.
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