A type of belly fat is linked to Alzheimer’s risk, research finds

People who have large amounts of fat stored around their organs as they age may be at higher risk of developing Alzheimer’s disease, a new study suggests.

This type of fat isn’t necessarily reflected in a high body-mass index.

Visceral fat, which can accumulate around the organs of even people at healthy BMIs, is associated with changes in the brain potentially decades before any symptoms of cognitive decline are seen, according to the study presented at the annual meeting of the Radiological Society of North America on Monday.

Visceral fat has previously been associated with systemic inflammation — which occurs when the immune system is constantly turned up even when there is no threat to health — and higher levels of insulin, both of which are thought to be involved in the development of Alzheimer’s, according to the study’s senior author, Dr. Cyrus Raji, a neuroradiologist at the Washington University School of Medicine in St. Louis.

“We need to move beyond traditional conceptions of body fat, like BMI, and really look at the specifics of how fat is distributed to understand the health risks,” Raji said.

While it takes an MRI scan of the abdomen to confirm a person has visceral fat, there can be signs, Raji said.

According to Raji, signs that you may have accumulated fat around your organs include:

• A waist that is larger than the hips.
• Blood sugar that is high enough for a diagnosis of diabetes or prediabetes.

More than 6 million people in the U.S. live with Alzheimer’s disease, according to the Alzheimer’s Association. The group estimates that by 2050 that number will rise to 13 million.

To take a closer look at the potential impact of visceral fat on the risk of Alzheimer’s, Raji and his colleagues analyzed data from 54 cognitively healthy volunteers ages 40 to 60 who had average BMIs of 32. A BMI of 30 or higher is considered obese, according to the Centers for Disease Control and Prevention.

The researchers measured a host of health parameters, including insulin and blood sugar levels. Using MRI scans, they assessed the amount of fat just under the skin, as well as what was surrounding the organs. MRIs were also used to measure the thickness of the cortex — the outer layer of the brain responsible for functions such as speech, perception, long-term memory and judgment — which becomes thinner as Alzheimer’s progresses.

PET scans were used in a subset of participants to determine whether two proteins associated with Alzheimer’s — tau and amyloid — were at higher levels.

When the researchers analyzed the fat measurements and the brain scans together, they found that participants with more visceral fat had larger accumulations of amyloid in their brains, suggesting that they might be at higher risk of developing Alzheimer’s disease.

Prior research has shown that inflammation and high levels of insulin, which can block the proteins that break down amyloid in the brain, are linked with visceral fat, Raji said.

Because the earliest development of Alzheimer’s in the brain can begin as much as 20 years before the first symptoms appear, the researchers plan to study the potential long-term impact of visceral fat by following up on the study’s participants.

“That’s why we started with a population at midlife,” Raji said. “We want to see how it might play a role in the development of Alzheimer’s, and that will give us an idea of the best window for effective interventions.”

The best way to lose visceral fat is through exercise, especially aerobic exercise, Raji said.

It’s not yet known whether getting rid of visceral fat can reverse its impact on the brain.

Dr. Mary Ellen Koran wasn’t surprised by the findings.

“Since we already know that visceral fat is linked to so many bad health outcomes, including those involving the heart, it makes sense that it’s also linked to poor brain health,” said Koran, an Alzheimer’s imaging specialist and an assistant professor of radiology and biological sciences at the Vanderbilt University Medical Center and School of Medicine. “But it’s important that we do studies like this to define that link.”

While it’s more likely that an obese person will have both types of fat, thin people can also have visceral fat but not realize it.

Koran said she’s seen “really skinny people who don’t have much subcutaneous fat but a bunch of fat around their organs.”

Still, Koran doesn’t recommend that people hoping to protect their brains get scanned for visceral fat until more research confirms the link.

While the number of people in the study is small, “it’s helpful that the researchers are looking at a younger group of people,” said Alzheimer’s specialist Dr. Joel Salinas, a neurologist at NYU Langone Health and chief medical officer at the Isaac Health Online Memory Clinic.

Knowing who is at risk will allow people to start treatments earlier, Salinas said. “You want to stop the fire before the building burns down.”

Dr. Borna Bonakdarpour, a neurology researcher at Northwestern University’s Feinberg School of Medicine, says the study doesn’t prove that visceral fat causes damage to the brain.

“It may simply be a marker for poor health,” Bonakdarpour said. “We know that people who don’t exercise or have a poor diet are at risk for developing Alzheimer’s.”

Before people start asking for abdominal scans to look for visceral fat, “we would need a much larger study,” said Dr. Fanny Elahi, a neurologist and Alzheimer’s researcher at the Icahn School of Medicine at Mount Sinai. “This is a very, very small study.”