In a new study, US researchers confirmed the known link between obesity and lower total brain volume and also found that abdominal fat in otherwise healthy middle aged people is associated with lower total brain volume, suggesting a greater risk of dementia  and Alzheimer's later on in life.

Results of the study, by Boston University School of Medicine (BUSM), are expected to be published today, 20 May, as an early online issue in the journal Annals of Neurology, the official journal of the American Neurological Association and the Child Neurology Society.

Senior author Dr Sudha Seshadri, associate professor of Neurology at BUSM, said in a statement that their results confirmed "the inverse association of increasing BMI with lower brain volumes in older adults and with younger, middle-aged adults".

She noted that this was the first study to do so in a much larger sample: previous studies have used data on up to 300 participants whereas for this study Seshadri and colleagues included over 700 individuals.

However, more importantly, said Seshadri:

"Our data suggests a stronger connection between central obesity, particularly the visceral fat component of abdominal obesity, and risk of dementia and Alzheimer's disease".

The 733 participants for this study were from the Framingham Heart Study Offspring Cohort. Their mean age was 60 and about 70 per cent were women.

The Framingham Heart Study started in 1948 with over 5,000 participating men and women from Framingham, Massachusetts whose data have been helping researchers do long term studies into factors that contribute to heart disease. The Offspring Cohort now follows the offspring of the original cohort and their spouses.

Seshadri and colleagues looked for associations between various body and brain measures.

For the body measures they included: Body Mass Index (BMI), waist circumference, waist to hip ratio, and measures of abdominal fat (called visceral adipose tissue or VAT) determined using computed tomography (CT) scans. They also took into account other physiology measures such as insulin resistance.

For the brain measures they included: magnetic resonance imaging (MRI) measures of total brain volume (TCBV), temporal horn volume (THV), and white matter hyperintensity volume (WMHV), and brain infarcts (brain damage caused by shortage of blood supply).

As well as confirming the link between increasing BMI and lower brain volume they found:

• A statistically significant link between abdominal fat (VAT) and lower total brain volume (TCBV).
   
• This link was independent of BMI and insulin resistance.
   
• No statistically significant link between abdominal fat (VAT) and temporal horn volume (THV), white matter hyperintensity volume (WMHV), or brain infarcts.