The six-year study involved 3,885 community dwelling people over age 65 in Chicago, IL. Of the participants, nearly 25 percent were obese with a body mass index (BMI) over 30, and 37 percent were overweight with a BMI between 25 and 29.9. Four cognitive tests were given at the beginning of the study and every three years thereafter over the six-year period.
The study found no significant changes in memory or cognitive function throughout the study for overweight or obese participants. In fact, participants who were underweight had more cognitive decline over time.
'We do not know yet why being overweight or obese does not increase the risk for cognitive decline in old age, however being underweight may be a correlate of the initial stages of Alzheimer's disease,' said study author Maureen T. Sturman, MD, MPH, Rush University Medical Center and John H. Stroger Hospital of Cook County in Chicago.
'While past studies have found obesity in middle age increases a person's risk for dementia or Alzheimer's disease, our findings show obesity in old age has no effect on a person's memory. These findings are consistent with previous studies showing that weight loss or low BMI in old age may be a precursor of cognitive decline or Alzheimer's disease.'