An analysis of the data of several studies shows a clear association between obesity and an increased risk for dementia, U.S. researchers say.

The Johns Hopkins Bloomberg School of Public Health researchers say subjects with a healthy body mass index and waist circumference saw a decreased risk for dementia than their counterparts with an elevated BMI or waist circumference.

"Preventing or treating obesity at a younger age could play a major role in reducing the number of dementia patients and those with other commonly associated illnesses such as Alzheimer's disease by up to 20 percent in the United States," senior author Dr. Youfa Wang said in a statement.

Lead researcher May A. Beydoun, Wang and H.A. Beydoun analyzed 10 previously published studies that examined the relationships between dementia or its subtypes and various measures of body fat. Based on a pooled analysis of their findings from seven of the studies, baseline obesity compared to normal weight increased the risk of Alzheimer's disease by 80 percent on average.

The team further concluded that being underweight also increases the risk of dementia and its subtypes.

The findings are published in the journal Obesity Reviews. (c) UPI