cardiothoracic radiologists find epicardial adipose tissue changes with the seasons
By Sam Marie Engle

Fat matters to Dr. Arthur Stillman, director of Emory Radiology’s Division of Cardiothoracic Imaging and an international leader in cardiovascular imaging with more than 188 publications. He is especially concerned about epicardial adipose tissue (EAT), the fat that surrounds the heart. When the fat is healthy, it protects the heart, but when it becomes dysfunctional, it promotes coronary artery disease.
Good or healthy EAT is beige: it contains brown fat with abundant mitochondria which are iron-rich, hence the brown color. These mitochondria allow brown fat to be metabolically active, which is why it helps maintain body temperature in cold conditions. Babies are born with a lot of brown fat to keep them warm; as we age, brown fat decreases. White fat, on the other hand, is composed of fatty acids and builds up when caloric intake exceeds energy needs. White fat, or subcutaneous adipose tissue (SCAT) is what fills the thighs, hips, and stomach and is what increases one’s risk of heart disease and type 2 diabetes. Brown fat diminishes as fat becomes dysfunctional and that leads to disease.
Several recent studies have shown that more radiodense EAT, fat more impenetrable by radiation, correlates with low coronary artery disease (CAD) risk while higher density EAT correlates with higher CAD risk. Dr. Stillman and his colleagues wanted to see if CT imaging could detect factors that affect the degree of EAT browning through seasonal variation. Those colleagues include John Archer, MD, Sagar Amin, MD, and Varuna Gadiyaram, MD, of Emory Radiology; Paolo Raggi, MD, PhD, of the Division of Cardiology in the Department of Medicine at the University of Alberta in Alberta, Canada; and Chao Zhang, PhD, of the Biostatistics Core in the Department of Pediatrics at Emory.
The researchers found that CT imaging of EAT radiodensity may not be used to reliably predict CAD risk because of this seasonal variation, which was not accounted for in prior studies. Just like brown fat in other parts of the body, EAT exhibits seasonal as well as gender and medication-related variations. For example, the researchers found that EAT gets browner in the winter but whiter in warmer months while no seasonal variation of radiodensity was observed for subcutaneous white fat. Similarly, testosterone promotes browning so men have more brown fat around the heart than women. Even certain medications affect browning; therefore, radiodensity of EAT measured by CT cannot reliably be used to assess cardiovascular health without taking into consideration these effects.
While these results might at first seem disappointing, Dr. Stillman is excited about them. “These findings tie together a lot of things we didn’t understand until now. We can use this knowledge to monitor the effect of drugs under investigation that promote browning of fat. These drugs can reduce obesity, diabetes, and cardiovascular risk.”
Dr. Stillman also points out how the study affirms the value of CT imaging for furthering such investigations. “The really good news for us as radiologists is that CT is an easy way to monitor the effects of those potential interventions because we can use CT to see that browning and beigeing of the epicardial adipose tissue.”
Access the research study, which was published online February 3rd by the peer-reviewed journal Atherosclerosis, here.
Good or healthy EAT is beige: it contains brown fat with abundant mitochondria which are iron-rich, hence the brown color. These mitochondria allow brown fat to be metabolically active, which is why it helps maintain body temperature in cold conditions. Babies are born with a lot of brown fat to keep them warm; as we age, brown fat decreases. White fat, on the other hand, is composed of fatty acids and builds up when caloric intake exceeds energy needs. White fat, or subcutaneous adipose tissue (SCAT) is what fills the thighs, hips, and stomach and is what increases one’s risk of heart disease and type 2 diabetes. Brown fat diminishes as fat becomes dysfunctional and that leads to disease.
Several recent studies have shown that more radiodense EAT, fat more impenetrable by radiation, correlates with low coronary artery disease (CAD) risk while higher density EAT correlates with higher CAD risk. Dr. Stillman and his colleagues wanted to see if CT imaging could detect factors that affect the degree of EAT browning through seasonal variation. Those colleagues include John Archer, MD, Sagar Amin, MD, and Varuna Gadiyaram, MD, of Emory Radiology; Paolo Raggi, MD, PhD, of the Division of Cardiology in the Department of Medicine at the University of Alberta in Alberta, Canada; and Chao Zhang, PhD, of the Biostatistics Core in the Department of Pediatrics at Emory.
The researchers found that CT imaging of EAT radiodensity may not be used to reliably predict CAD risk because of this seasonal variation, which was not accounted for in prior studies. Just like brown fat in other parts of the body, EAT exhibits seasonal as well as gender and medication-related variations. For example, the researchers found that EAT gets browner in the winter but whiter in warmer months while no seasonal variation of radiodensity was observed for subcutaneous white fat. Similarly, testosterone promotes browning so men have more brown fat around the heart than women. Even certain medications affect browning; therefore, radiodensity of EAT measured by CT cannot reliably be used to assess cardiovascular health without taking into consideration these effects.
While these results might at first seem disappointing, Dr. Stillman is excited about them. “These findings tie together a lot of things we didn’t understand until now. We can use this knowledge to monitor the effect of drugs under investigation that promote browning of fat. These drugs can reduce obesity, diabetes, and cardiovascular risk.”
Dr. Stillman also points out how the study affirms the value of CT imaging for furthering such investigations. “The really good news for us as radiologists is that CT is an easy way to monitor the effects of those potential interventions because we can use CT to see that browning and beigeing of the epicardial adipose tissue.”
Access the research study, which was published online February 3rd by the peer-reviewed journal Atherosclerosis, here.