Obesity may increase adults’ risk for having dementia, according to researchers at the Johns Hopkins Bloomberg School of Public Health. Their analysis of published obesity and dementia prospective follow-up studies over the past two decades shows a consistent relationship between the two diseases.

Obesity increases the risk of dementia in general by 42 percent, Alzheimer's by 80 percent and vascular dementia by 73 percent, the new review suggests. Being underweight increases the general dementia risk by 36 percent. But researchers who carried out an international review of research since 1995 found no elevated risk in people who were normal or overweight.

“Our analysis of the data shows a clear association between obesity and an increased risk for dementia and several clinical subtypes of the disease,” said Youfa Wang, MD, PhD, senior author of the study and associate professor with the Bloomberg School’s Center for Human Nutrition. “Subjects with a healthy body mass index (BMI) and waist circumference saw a decreased risk for dementia than their counterparts with an elevated BMI or waist circumference.” Wang adds, “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.”

Lead researcher May A. Beydoun, along with Wang and H.A. Beydoun attribute these findings to a systematic review of 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 7 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 studies cited in the meta-analysis were conducted in a number of countries, including the United States, Finland, Sweden and France, and contained middle-aged and older adults.

Previously published research defines dementia as not a single disorder, but a number of syndromes characterized by diverse behavioral, cognitive, and emotional impairments. The most common form is Alzheimer’s disease, with an estimated 5 million adults living with the disease in the United States alone.

“Currently, Alzheimer’s disease is the eighth leading cause of death among the elderly population in the United States. While more studies are needed to determine optimal weight and biological mechanisms associated with obesity and dementia, these findings could potentially decrease the number of people diagnosed with dementia and lead to an overall better quality of life,” said May A. Beydoun, a former postdoctoral research fellow at the Johns Hopkins Bloomberg School of Public Health.

"Obesity and central obesity as risk factors for incident dementia and its subtypes: a systematic review and meta-analysis" was written by M. A. Beydoun, H. A. Beydoun and Y. Wang.

The research was funded by the Johns Hopkins Bloomberg School of Public Health.