Middle-aged people with thick waist or pot belly are nearly three times more likely to suffer from Alzheimer's disease or other dementia in their 70s and 80s than people with little to no belly fat, according to a new study.

The new study - published today in Neurology, the journal of the American Academy of Neurology - suggests that the effect of fat on the body can cause more complications than previously thought. Even people who weren't overweight were susceptible to such diseases.

That abdominal fat, which makes our body apple-shaped rather than pear-shaped, has already been linked to higher risk of developing diabetes, stroke and heart disease.

Rachel Whitmer, a research scientist at Kaiser's Division of Research in Oakland and lead author of the study said people with pear-shaped bodies tend to carry most of their weight below the waist, in the hips, buttocks and thighs as compared to people with apple-shaped bodies that have more visceral fat.

Researchers believe that the visceral fat is metabolically active and it may release toxins associated with atherosclerosis or plaque build-up in the brain - the main reason for Alzheimer's disease.

The Kaiser study involved 6,583 men and women who were ages 40 to 45 when they had checkups between 1964 and 1973. Of the 6,583 patients studied, 15.9 percent had been diagnosed with dementia by 2006.

Among patients with the most visceral fat in middle age, the rate of dementia was 324.3 cases per 10,000; patients with the least belly fat had a rate of dementia of 214.6 cases per 10,000. The study concluded that people with the most belly fat were 2.72 times more likely to develop dementia than those with the least fat.

The study also found that patients who were of average weight but has belly fat were 89 percent more likely to develop dementia than people of average weight with little or no belly fat.

Dementia is the progressive decline in cognitive function due to damage or disease in the brain beyond what might be expected from normal aging. Although dementia is far more common in the geriatric population, it may occur in any stage of adulthood. This age cutoff is defining, as similar sets of symptoms due to organic brain dysfunction are given different names in populations younger than adulthood.