Increasing rates of obesity have led to concerns about an epidemic of adverse health consequences. Obesity is most simply characterized by measuring waist circumference or waist to hip ratio (WHR). The frequent association of abdominal obesity, as determined by the WHR, with elevation of serum triglycerides, decline in HDL (the "good cholesterol"), hypertension and diabetes constitute a metabolic constellation often referred to as Syndrome X, or the Metabolic Syndrome. It is an important risk factor for cardiovascular disease and stroke.

Obesity has been linked to the development of Alzheimer disease and specific changes in brain structure. Based on the correlation between obesity, dementia and cardio-metabolic factors, investigations have focused on defining potential alterations in brain anatomy seen in this context. Magnetic Resonance Imaging (MRI) was chosen as the desired imaging modality because of its capacity for high spatial resolution and quantitative assessment.

MRI measures that have been previously linked to cognitive impairment and dementia include  hippocampal volume (HV) and white matter hyperintensities (WMH). The hippocampus is a region of the brain essential for memory processing and retrieval. Cerebral white matter consists of nerve cell processes that serve to connect distant clusters of neurons into functional networks. Decreases in HV and and increases in WMH have been shown to contribute independently to the risk of dementia. Because WHR is a component of the Metabolic Syndrome, associations between it and these structural brain changes were investigated.

A recent study was conducted in the Central Valley of California including 112 individuals in the Latino community. WHR determinations, MRI scans and metabolic assessments were performed.  In this cross-sectional analysis greater WHR was associated with a fall in HV and an increase in WMH. A one standard deviation increase in WHR was associated with a 27% increase in WMH. It is important to note that these relationships were not affected by adjustment for body mass index (BMI) (a measure of generalized obesity), total cholesterol level, fasting blood glucose, serum insulin levels or systolic blood pressure.

Although prior studies have shown correlations between HV and WMH with various metabolic and cardiovascular factors, in this study they did not explain the entire association. The authors suggested other potential etiologies such as inflammatory mechanisms linked to the central fat depots, stress and elevation of the stress hormone cortisol as additional factors.

These findings complement a large body of data that demonstrate the negative effects of obesity on cognitive function. They are also consistent with the emerging reports of the beneficial effects of exercise on cognition. One result of exercise may be improved weight regulation. Taken together, these findings provide further support for the suggestion that structural brain changes might be at least partially modifiable by lifestyle alterations.