Obesity Linked to Mental Decline

Oct. 18, 2006 — Adding to the litany of health problems linked to obesity, the results of a five-year study suggest that a high body mass index may impair cognitive abilities in middle-aged adults.

A measurement of body fat based on height and weight, BMI is used to determine overweight and obesity. A BMI of 25 or more is considered overweight, while 30 or more marks the obese range.

In 1996 and again in 2001, the researchers collected medical, psychosocial and environmental data from 2,223 healthy workers aged 32 to 62. A battery of tests measured a range of cognitive abilities in the study participants.

"Cross-sectionally, a higher BMI was associated with lower cognitive scores after adjustment for age, sex, educational level, blood pressure, diabetes, and other psychosocial co-variables," reported Maxime Cournot, an epidemiologist at Toulouse University School of Medicine in France, and colleagues in the current issue of Neurology.

Lower cognitive scores in overweight and obese people were particularly apparent in a test involving the memorization of word lists. Participants were given a list of 16 words and asked to remember them immediately and again after a delay.

While people in the lowest BMI range (15 to 21.5) remembered on average 9 of 16 words, those in the highest range (27.7 to 45) remembered only seven words on average.

What's more, individuals with the highest BMIs showed greater cognitive decline five years later — their recall dropped from 44 percent to 37.5 percent on average. On the contrary, subjects in the low-BMI range maintained the same level of recall.

"The key point of this study is that midlife issues like obesity have an impact on cognition," David Knopman, a professor of neurology at Mayo Clinic College of Medicine, told Discovery News. "Presumably these negative influences on the brain are cumulative over a lifetime and increase a person's risk of developing dementia later in life."

According to Knopman, it is not unexpected that obesity is associated with cognitive decline.

"Obesity is a marker or proxy for diabetes and hypertension, which have been repeatedly shown to be associated with cognitive decline in middle age and elderly," he explained.

The findings were echoed by another study published in the same journal, which showed physical fitness is associated with the preservation of cognitive function over time.

In that study, researchers at the University of Edinburgh in Scotland analyzed 460 men and women who, at age 11, had taken part in the Scottish Mental Survey of 1932. The partecipants were tested again using the same cognitive test at age 79.

It emerged that physical fitness contributes to better cognitive ability in old age.

"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," main author Ian Deary said in a statement.