Having belly fat not only poses aesthetic concerns, but also affects a person's health by elevating the risk of diabetes, stroke and heart disease. According to a new study, higher amounts of visceral abdominal fat in the middle ages raises the risk of Alzheimer's disease.

Visceral fat is a hidden fat found deep within a person's abdominal cavity that wraps the internal organs, including the liver and intestines. Some levels of visceral fat help to protect the organs, but too much of it is a sign of metabolic syndrome associated with high blood pressure, obesity, high cholesterol and insulin resistance. Visceral fat gets stored when a person eats too many calories and takes too little exercise.

Researchers found a link between these hidden fats and changes in the brain associated with Alzheimer's, which might help to predict the condition even 15 years before the earliest symptoms appear. The findings will be presented next week at the annual meeting of the Radiological Society of North America (RSNA).

"Even though there have been other studies linking BMI with brain atrophy or even a higher dementia risk, no prior study has linked a specific type of fat to the actual Alzheimer's disease protein in cognitively normal people. Similar studies have not investigated the differential role of visceral and subcutaneous fat, especially in terms of Alzheimer's amyloid pathology, as early as midlife," said study author Mahsa Dolatshahi, from Washington University School of Medicine in St. Louis, in a news release.

More than 6 million people in the U.S. live with Alzheimer's disease, a progressive condition that affects a person's memory, thoughts and ability to carry out conversations. The number is expected to rise to nearly 13 million by 2050, according to the Alzheimer's Association.

The research team evaluated 54 cognitively healthy participants between the ages of 40 to 60, with an average BMI of 32. The participants' brain volumes were measured using MRI and the presence of amyloid and tau (proteins in the brain associated with Alzheimer's) were determined using position emission tomography (PET) scans.

To identify the risk of Alzheimer's, the researchers estimated the associations with factors such as body mass index (BMI), obesity, insulin resistance and abdominal adipose (fatty) tissue.

"The researchers found that a higher visceral to subcutaneous fat ratio was associated with higher amyloid PET tracer uptake in the precuneus cortex, the region known to be affected early by amyloid pathology in Alzheimer's disease. This relationship was worse in men than in women," the news release read.

The study also found an association between higher abdominal fat and an increase in brain inflammation, which is associated with an increased risk of Alzheimer's.

"Several pathways are suggested to play a role. Inflammatory secretions of visceral fat — as opposed to potentially protective effects of subcutaneous fat — may lead to inflammation in the brain, one of the main mechanisms contributing to Alzheimer's disease," Dolatshahi said.

"This study highlights a key mechanism by which hidden fat can increase the risk of Alzheimer's disease. It shows that such brain changes occur as early as age 50, on average—up to 15 years before the earliest memory loss symptoms of Alzheimer's occur," senior author Cyrus A. Raji said.