Researchers from the University of Arizona have found that having a higher body mass index, or BMI, can negatively impact cognitive functioning in older adults.

‘The higher your BMI, the more your inflammation goes up,’ explained Kyle Bourassa, lead author of the study, which is 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 also have linked higher BMI to lower cognitive functioning. But how and why the two are connected was far less clear.

‘We saw this effect, but it’s a black box. What goes in between?’, said Kyle, a UA psychology doctoral student.

‘Establishing what biologically plausible mechanisms explain this association is important to be able to intervene later.’

Kyle and his co-author, UA Psychology Professor David Sbarra, analysed data from the English Longitudinal Study of Aging, which includes over 12 years’ worth of information on the health, wellbeing and social and economic circumstances of the English population age 50 and older.

Using two separate samples from the study – one of about 9,000 people and one of about 12,500 – researchers looked at aging adults over a six-year period. They had information on study participants’ BMI, inflammation and cognition, and they found the same outcome in both samples.

‘The higher participants’ body mass at the first time point in the study,’ Kyle said, ‘the greater the change in their CRP levels over the next four years. 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.’

The findings support existing literature linking inflammation to cognitive decline and take it a step further by illuminating the important role of body mass in the equation.

However, David added a word of caution in trying to understand the findings, saying, ‘The findings provide a clear and integrative account of how BMI is associated with cognitive decline through systemic inflammation, but we need to remember that these are only correlational findings.

‘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.