Add another hazard to the pitfalls of being
overweight -- a few extra pounds might reduce
your brainpower.
According to a new French study, heftier
people score lower on cognitive tests, even
when factors such as education level are taken
into account.
The effect appears to be quite small, however.
"These tests are sensitive enough to
detect small variations in scientific studies.
However, in a middle-aged, healthy, active
population, these differences in the cognitive
performances may be hardly perceived by individuals,"
said study author Dr. Maxime Cournot, a researcher
with the Toulouse University Hospital and
the National Institute of Health and Medical
Research in France.
The findings are published in the Oct. 10
issue of Neurology.
Following up on previous studies linking
weight and cognition, the new study aimed
to find out if there is a connection in middle-aged
healthy people.
To do so, the researchers analyzed statistics
from a survey of 2,223 salaried French workers
in 1996 and 2001. The workers were between
32 and 62 years old in 1996.
The study authors first calculated each participant's
body-mass index (BMI), a ratio of weight and
height. For reference, a 5-foot-5-inch woman
weighing 139 pounds has a BMI of 23, which
is considered normal. Statistical overweight
begins at a BMI of 25, and obesity starts
at BMI 30 or over.
The team then compared BMI to the results
of cognitive tests.
People with higher BMIs scored lower on cognitive
tests that examined memory, attention and
thought-processing. For example, people on
the thin side -- with a BMI of 20 -- remembered
an average of nine of 16 words in a memory
test. On the other hand, those with a BMI
of 30 remembered an average of seven words.
Those with higher BMIs also scored lower
on the tests five years later.
The differences held up even when the numbers
were adjusted for the possible influences
of education level, age, gender and other
factors.
The cognitive differences were very modest,
Cournot said, but "slight consequences"
linked to poorer cognition ability are still
possible, she said.
How might obesity affect the brain? It's
possible that excess weight could help clog
the arteries in the brain just as it does
in the heart, Cournot said. It's also possible,
she added, that obesity could disrupt hormones
such as insulin that affect brain cells.
Dr. David Knopman, a professor of neurology
at Mayo Clinic College of Medicine, is familiar
with the findings. He said the real culprits
could be diabetes and high blood pressure,
both of which are "more strongly and
consistently linked to both cognitive decline
and dementia risk."
Interestingly, people who became more overweight
slowly over time didn't show higher levels
of cognitive difficulties. That could be because
the subjects weren't studied long enough or
because the study wasn't designed to pick
up such gradual changes, Cournot said.
According to Knopman, it's also possible
that whatever process links obesity and mental
skills had set in much earlier.
The study results need to be confirmed by
other researchers, Cournot said, but they
still support the general recommendation that
people eat right and exercise to avoid obesity.
Knopman agreed. The study findings suggest
that "obesity in midlife may have long
term consequences for the brain, not just
for the heart," he said.
Another study in Neurology echoed
the French findings. Researchers at the University
of Edinburgh, Scotland, found that mental
fitness in old age is closely connected to
physical fitness and intelligence levels in
childhood.
The study was based on an analysis of 460
Scottish people who took part in a study in
1932 as children and then were tested again
at age 79.
"Fitness contributes to better cognitive
ability in old age," study author Ian
Deary concluded in a prepared statement. "Thus,
[of] two people starting out with the same
IQ at age 11, the fitter person at age 79
will, on average, have better cognitive function."
