TUESDAY, Oct. 10, 2006 (HealthDay News) -- 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."
Learn more about weight gain from the American Obesity Association.