Obesity has been linked to cognitive decline, but a new study involving 300 post-menopausal women has found that higher BMI was associated with higher cognitive scores.
Of the 300 women (average age 60), 158 were classified as obese (waist circumference of at least 88cm, or BMI of over 30). Cognitive performance was assessed in three tests: The Mini-Mental Statement Examination (MMSE), a clock-drawing test, and the Boston Abbreviated Test.
Both BMI and waist circumference were positively correlated with higher scores on both the MMSE and a composite cognitive score from all three tests. It’s suggested that the estrogen produced in a woman’s fat cells help protect cognitive function.
Interestingly, a previous report from the same researchers challenged the link found between metabolic syndrome and poorer cognitive function. This study, using data from a large Argentinean Cardiovascular Prevention Program, found no association between metabolic syndrome and cognitive decline — but the prevalence of metabolic syndrome and cognitive decline was higher in males than females. However, high inflammatory levels were associated with impairment of executive functions, and higher systolic blood pressure was associated with cognitive decline.
It seems clear that any connection between BMI and cognitive decline is a complex one. For example, two years ago I reported that, among older adults, higher BMI was associated with more brain atrophy (replicated below; for more recent articles relating obesity to cognitive impairment, click on the obesity link at the end of this report). Hypertension, inflammation, and diabetes have all been associated with greater risk of impairment and dementia. It seems likely that the connection between BMI and impairment is mediated through these and other factors. If your fat stores are not associated with such health risk factors, then the fat in itself is not likely to be harmful to your brain function — and may (if you’re a women) even help.
Overweight and obese elderly have smaller brains
Analysis of brain scans from 94 people in their 70s who were still "cognitively normal" five years after the scan has revealed that people with higher body mass indexes had smaller brains on average, with the frontal and temporal lobes particularly affected (specifically, in the frontal lobes, anterior cingulate gyrus, hippocampus, and thalamus, in obese people, and in the basal ganglia and corona radiate of the overweight). The brains of the 51 overweight people were, on average, 6% smaller than those of the normal-weight participants, and those of the 14 obese people were 8% smaller. To put it in more comprehensible, and dramatic terms: "The brains of overweight people looked eight years older than the brains of those who were lean, and 16 years older in obese people." However, overall brain volume did not differ between overweight and obese persons. As yet unpublished research by the same researchers indicates that exercise protects these same brain regions: "The most strenuous kind of exercise can save about the same amount of brain tissue that is lost in the obese."
Zilberman, J.M., Del Sueldo, M., Cerezo, G., Castellino, S., Theiler, E. & Vicario, A. 2011. Association Between Menopause, Obesity, and Cognitive Impairment. Presented at the Physiology of Cardiovascular Disease: Gender Disparities conference, October 12, at the University of Mississippi in Jackson.
Vicario, A., Del Sueldo, M., Zilberman, J. & Cerezo, G.H. 2011. The association between metabolic syndrome, inflammation and cognitive decline. Presented at the European Society of Hypertension (ESH) 2011: 21st European Meeting on Hypertension, June 17 - 20, Milan, Italy.
(2010). Brain structure and obesity.
Human Brain Mapping. 31(3), 353 - 364.