Watch Your Waist to Save Your Brain

Summarized by Robert W. Griffith, MD
April 10, 2006

Introduction

Both obesity and Alzheimer's disease are increasing in frequency. Is there a link? It seems very possible; there are numerous factors common to both conditions: diabetes, high blood pressure, and vascular disease, to name a few.
A study reported last year has strengthened the likelihood of a link between obesity and mental deterioration (called cognitive decline) leading to dementia. It was done at UCLA Davis, California, and reported in the Archives of Neurology; we summarize it here.

What was done

The scientists decided to use the waist:hip ratio (WHR) as their measure of overweight, because so-called abdominal obesity is one factor in the metabolic syndrome¹, and more commonly used than the body mass index (BMI) or simple weight for predicting cardiovascular problems.

They examined 112 people selected from a larger group (1750) of over-60 Latino individuals living in California Central Valley. The WHR was measured twice, and averaged; the waist was measured at the midpoint between the top of the pelvis and the lower edge of the ribs; the hip measurement was the maximum circumference over the buttocks below the top of the pelvis.

Blood pressure was measured in the arm and at the ankle; fasting blood sugar, insulin, and total cholesterol were determined.

Cognitive impairment was considered to be represented by magnetic resonance imaging (MRI) of the brain, measuring the volume of one part of the brain (the hippocampus) and the hyperintensity of the white matter; these are abbreviated to HV and WMH, respectively. The investigators had previously demonstrated that HV and WMH both contribute independently to the risk of dementia.

What was found

The average age of the participants was 70. Their average weight was 76 kg (168 pounds), and their average BMI was 29.2 (25% of them were over 30, i.e. 'obese'). The average WHR was 0.91, ranging from 0.75 to 1.14. The average fasting glucose level was 122 mg/dL (6.8 mmol/L), which reflected the 39% frequency of type 2 diabetes in this population/age group.

Ten percent of the subjects had cognitive impairment but did not have dementia, and an additional 21% had dementia. While there was no significant association between these conditions and WHR, analysis for links between WHR and the HV and WMH values obtained on MRI was more revealing.

There was an age-related decrease in HV, but in addition there was an independent WHR-related decrease; increasing age and increasing waist-hip ratio were both associated with a decrease in hippocampal volume, suggestive of cognitive impairment.

Similarly, there were age-related increases in WMH with increased age and increased WHR - again, independently of each other. Thus increased age and increased waist-hip ratio were both associated with an increase in white matter hyperintensity on MRI, another indicator of cognitive decline.

Of the other 'metabolic syndrome' factors analyzed (1), only the fasting blood glucose and the systolic blood pressure were linked to an increased WHR.

What these findings mean

This study shows that the distribution and amount of body fat accounted for a small but significant variation in the size of the hippocampus and the amount of white matter hyperintensity in the brain. Although small, the brain changes were such that, roughly speaking, a 10% increase in the measured waist-hip ratio (i.e. central adiposity) was associated with a 25% increase in white matter hyperintensity and a corresponding reduction in volume of the hippocampus, an important part of the brain.

What does this mean? In short, abdominal fat increases your risk of developing Alzheimer's disease or another form of dementia. Another reason to keep your weight under control!

Source

• Central obesity and the aging brain. W. Jagust, D. Harvey, D. Mungas, M. Haan, Arch Neurol, 2005, vol. 62, pp. 1545--1548

Footnotes
1. The metabolic syndrome requires 3 of the following risk factors to be present: (a) Waist size over 40 inches (102 cm) in men, or 35 inches (88 cm) in women. (b) Serum triglyceride level over 150 mg/dL (1.7 mmol/L). (c) Serum HDL ('good') cholesterol below 40 mg/dL (1.0 mmol/L) in men, or 50 mg/dL (1.29 mmol/L) in women. (d) Blood pressure over 130/85 mm Hg (either number), or being on blood pressure medication. (e) Fasting blood sugar over 110 mg/dL (6.1 mmol/L). Take the self-test, at the link below.

Related Links
The Metabolic Syndrome and the Risk of Alzheimer's
Physical Fitness Can Fight Off Dementia
Tool: Do You Have the Metabolic Syndrome?

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