A study to be presented at the RSNA meeting shows that higher levels of abdominal visceral fat accumulated in midlife are associated with an increased risk of developing Alzheimer's disease. The study, which used brain scans on 54 participants, showed that this fat type is associated with early brain changes and inflammation, highlighting its potential as an intervention target for early Alzheimer's disease.
Higher levels of abdominal visceral fat in middle age are linked to the onset of Alzheimer's disease, according to a study to be presented next week at the annual meeting of the Radiological Society of North America (RSNA). Visceral fat is the fat deep in the abdomen around the internal organs. Researchers have found that this hidden belly fat is linked to changes in the brain that precede the earliest symptoms of memory loss in Alzheimer's disease by 15 years.
According to the Alzheimer's Association, more than 6 million Americans currently have Alzheimer's disease. This number is expected to rise to nearly 13 million by 2050. One in five women and one in ten men will develop Alzheimer's disease in their lifetime.
Identifying early Alzheimer's risk
To detect Alzheimer's risk early, researchers evaluated the relationship between brain MRI volume, amyloid and tau uptake in positron emission tomography (PET) and body mass index (BMI), adiposity, insulin resistance and abdominal adipose tissue in cognitively normal middle-aged people. Amyloid and tau proteins are thought to interfere with communication between brain cells.
Unique study on fat types and Alzheimer's risk
"While other studies have linked body mass index (BMI) to brain shrinkage and even a higher risk of dementia, no previous studies have linked specific types of fat to actual Alzheimer's disease proteins in people with normal cognition," said study author Mahsa Dolatshahi, MD, a postdoctoral fellow at the Mallinckrodt Institute of Radiology (MIR) at Washington University School of Medicine in St. Louis. "Similar studies have not investigated the differential roles of visceral and subcutaneous fat, particularly in Alzheimer's amyloid pathology, as early as middle age."
Research methods and results
In this cross-sectional study, researchers analyzed data from 54 cognitively healthy participants, who ranged in age from 40 to 60 years old and had an average body mass index of 32. Participants underwent glucose and insulin measurements and a glucose tolerance test. Abdominal MRI measures the volume of subcutaneous fat (subcutaneous fat) and visceral fat. Brain MRI measures the thickness of the cerebral cortex affected by Alzheimer's disease. Positron emission computed tomography (PET) scans were used to examine disease pathology in a subset of 32 participants, focusing on the amyloid plaques and tau nodules that accumulate in Alzheimer's disease.
The researchers found that the higher the ratio of visceral fat to subcutaneous fat, the higher the amyloid PET tracer uptake in the precuneus cortex. This relationship is stronger in men than in women. The researchers also found that higher visceral fat measurements were associated with increased inflammatory burden in the brain.
"Several pathways are thought to play a role," said Dr. Dolatshahi. "Inflammatory secretion of visceral fat - as opposed to the potentially protective role of subcutaneous fat - may contribute to inflammation in the brain, which is one of the major mechanisms leading to Alzheimer's disease."
Impact on early diagnosis and intervention
Senior author Cyrus A. Raji, MD, associate professor of radiology and neurology and director of neuromagnetic resonance imaging at the Institute of Medicine. He said: "This study highlights a key mechanism by which hidden fat can increase the risk of Alzheimer's disease. It shows that this brain change occurs as early as age 50 on average, 15 years before the earliest symptoms of Alzheimer's memory loss. The findings may show that visceral Fat is a therapeutic target to modify future brain inflammation and dementia risk. By looking beyond body mass index to better characterizing the anatomical distribution of body fat on MRI, we now have a uniquely better understanding of why this factor may increase Alzheimer's disease risk."