Study of Over 50,000 People Finds Brown Fat May Protect Against Chronic Diseases

A new study in Nature Medicine finds that, among over 52,000 participants, individuals who had detectable brown fat were less likely than their peers to suffer cardiac and metabolic conditions ranging from Type II diabetes to coronary artery disease, which is the leading cause of death in the United States.

The study, by far the largest of its kind in humans, confirms and expands the health benefits of brown fat suggested by previous studies. "For the first time, it reveals a link to lower risk of certain conditions," said Paul Cohen, the Albert Resnick, M.D., assistant professor and senior attending physician at The Rockefeller University Hospital. "These findings make us more confident about the potential of targeting brown fat for therapeutic benefit."

Brown vs white fat

Brown fat, unlike white fat, is a magical tissue that you would want more of. It burns energy and scientists hope that one day it may hold the key to new obesity treatments.

Whilst brown fat has been studies in newborns and animals for many years, it was only in 2009 that scientists appreciated it can also be also found in some adults, typically around the neck and shoulders. From then on, researchers have scrambled to study the elusive fat cells, which possess the power to burn calories to produce heat in cold conditions.

Large-scale study of brown fat

Large-scale studies of brown fat have been challenging as this tissue shows up only on PET scans, a special type of medical imaging that is expensive and uses radiation. Therefore, scientists do not wish to expose healthy individuals to this type of scan if it can be avoided.

A physician-scientist, Becher came up with an alternative. Right across the street from his lab, many thousands of people visit Memorial Sloan Kettering Cancer Center each year to undergo PET scans for cancer evaluation. Becher knew that when radiologists detect brown fat on these scans, they routinely make note of it to make sure it is not mistaken for a tumor. "We realized this could be a valuable resource to get us started with looking at brown fat at a population scale," Tobias Becher, the study's first author and formerly a clinical scholar in Cohen's lab, said.

Working with Heiko Schoder and Andreas Wibmer at Memorial Sloan Kettering, the scientists reviewed 130,000 PET scans from over 52,000 patients. They found the presence of brown fat in nearly 10 percent of individuals, which Cohen believes is likely an underestimate because the patients had been instructed to avoid cold exposure, exercise, and caffeine – all of which are thought to increase brown fat activity.

Several common and chronic diseases were less prevalent among people with detectable brown fat. For example, only 4.6% had Type II diabetes, compared with 9.5% of individuals who did not have detectable brown fat. Similarly, 18.9% had abnormal cholesterol, compared to 22.2% in those without brown fat.

The study identified three more conditions for which people with brown fat have lower rare at lower risk of experiencing:

• Hypertension
   
• Coronary artery disease
  
  
• Congestive heart failure

Brown fat may also mitigate the adverse health effects of obesity. Obese people generally have an increased risk of heart and metabolic conditions. In this study, the researchers found that, in obese people with brown fat, the prevalence of these conditions was similar to that of non-obese people. "It almost seems like they are protected from the harmful effects of white fat," Cohen said.

More than an energy burning powerhouse

How, exactly, brown fat may contribute to better health remains unclear, but there are some ideas; brown-fat cells eat up glucose in order to burn calories, and it's possible that this lowers blood glucose levels – a major risk factor for developing diabetes.

In other conditions such as hypertension, which is tightly connected to the hormonal system, brown fat's role is somewhat more mysterious. Cohen said, "We are considering the possibility that brown fat tissue does more than consume glucose and burn calories, and perhaps actually participates in hormonal signaling to other organs."

"The natural question that everybody has is, 'What can I do to get more brown fat?'" Cohen said. "We don't have a good answer to that yet, but it will be an exciting space for scientists to explore in the upcoming years."

The researchers plan to look for genetic variants that may explain why some people have more of it than others. This is a potential first step towards the development of pharmacological interventions to stimulate brown fat activity. 

Reference: Becher T, Palanisamy S, Kramer DJ, et al. Brown adipose tissue is associated with cardiometabolic health. Nature Medicine. 2021. doi:10.1038/s41591-020-1126-7.