"The higher your BMI, the more your inflammation goes up," said Kyle Bourassa, lead author of the study (which was published in the journal Brain, Behavior and Immunity). "Prior research has found that inflammation -- particularly in the brain -- can negatively impact brain function and cognition."
Previous studies have also linked higher BMI – which is a value derived from the mass and height of an individual – to lower cognitive functioning. But how BMI is connected to cognitive functioning is far less clear.
"We saw this effect, but it's a black box. What goes in between?" said Bourassa, a third year graduate student in the University of Arizona’s clinical psychology PhD program. "Establishing what biologically plausible mechanisms explain this association is important to be able to intervene later."
Bourassa and his co-author, University of Arizona psychology professor David Sbarra, analyzed data from the English Longitudinal Study of Aging, which includes over 12 years' worth of information on the health, well-being, and socioeconomic circumstances of the English population aged 50 and older.
The researchers used two separate samples from the study – one of about 9,000 people and one of about 12,500 people – to assess aging adults over a six-year period. The researchers also had information on the participants’ body mass index, inflammation and cognition. Bourassa and Sbarra found the same outcomes in both samples.
"The higher [a] participants' body mass at the first time point in the study, the greater the change in their CRP levels over the next four years,” Bourassa said. “CRP stands for C-reactive protein, which is a marker in the blood of systemic inflammation in your body. Change in CRP over four years then predicted change in cognition six years after the start of the study. The body mass of these people predicted their cognitive decline through their levels of systemic inflammation."
Sbarra added a word of caution when drawing final conclusions. He noted that while the study provided a clear and integrative account of how BMI is associated with cognitive decline via systematic inflammation, he urged the public to remember that the findings are only correlational.
"Of course, correlation does not equal causation. The findings suggest a mechanistic pathway, but we cannot confirm causality until we reduce body mass experimentally, then examine the downstream effects on inflammation and cognition," Sbarra said.
Researchers from the University of Arizona have found that having a higher body mass index (BMI) can negatively impact cognitive functioning in older adults. The most likely culprit for this impairment is inflammation.