Brown fat associated with less heart and metabolic disease

In these PET scans, the person on the left has abundant brown fat around the neck and cervical spine. The person on the right has no detectable brown fat. Andreas G. Wibmer and Heiko Schöder, Memorial Sloan Kettering Cancer Center

Too much white fat, a characteristic of obesity, has been shown to increase the risk of type 2 diabetes, high blood pressure, and other diseases. A less common type of fat, called brown fat, uses blood sugar and fat molecules to create heat and help maintain body temperature. Studies suggest it may have beneficial health effects.

Researchers have been interested in the potential of harnessing brown fat as a treatment for diseases related to obesity. But whether it actually contributes to better health has been unclear. Measuring brown fat requires a type of imaging called a PET scan. Because PET scans use radiation, researchers don’t want to use them in healthy people.

However, people with cancer often undergo PET scanning to track tumors before, during, or after treatment. At some institutions, doctors reading these scans routinely mark areas of brown fat to prevent them from being mistaken for tumors.

A research team led by Dr. Paul Cohen from the Rockefeller University examined such scans from more than 50,000 people seen at Memorial Sloan Kettering Cancer Center during the last ten years. Brown fat was marked on scans taken from about 10% of the patients.

The researchers compared the prevalence of several heart and metabolic diseases between people with brown fat and a matched group who didn’t have measurable brown fat. They matched people by sex, age, body-mass index (BMI), and the outdoor temperatures at the time the scans were taken, which can also affect brown fat.

The team adjusted for factors thought to either decrease or increase the potential for brown fat production. These included the use of some medications, such as beta blockers and statins, and different cancer treatments.

The study was funded in part by NIH’s National Center for Advancing Translational Sciences (NCATS). Results were published on January 4, 2021, in Nature Medicine.

The team found that people with brown fat were less likely to have type 2 diabetes, cardiovascular disease, harmful levels of blood cholesterol and fats, heart failure, or high blood pressure.

This reduced risk was observed even among people who were obese or overweight. Overall, the researchers saw the prevalence of heart and metabolic diseases rise with increasing BMI. However, this rise was tempered in people with brown fat. For example, about 20% of obese participants without brown fat had type 2 diabetes. In comparison, less than 8% of obese participants with measurable brown fat had the condition.

Blood samples showed that the presence of brown fat was linked with better blood sugar control and improved levels of triglycerides (a kind of fat) and high-density lipoprotein (“good” cholesterol). Brown fat was also associated with differences in levels of some types of immune and blood cells. This suggests that brown fat may have effects on the body outside of metabolism.

The study revealed a link between brown fat and lower risk of certain conditions. “The natural question that everybody has is, ‘What can I do to get more brown fat?’” Cohen says. “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.”

—by Sharon Reynolds