Fatty muscle raises chances of developing heart disease

People with pockets of fat inside their muscles are at a higher risk of mortality or hospitalisation from a heart attack or heart failure, regardless of their body mass index, according to research published in the European Heart Journal .

The finding adds evidence that existing measures, such as body mass index or waist circumference, are not adequate to evaluate the risk of heart disease accurately for all people.

Study leader Prof Viviany Taqueti of Brigham and Women’s Hospital and Faculty at Harvard Medical School, Boston, said body mass index  remains a controversial and flawed marker of cardiovascular prognosis. This is especially true in women, where high body mass index may reflect more ‘benign’ types of fat.

“Intermuscular fat can be found in most muscles in the body, but the amount of fat can vary widely between different people. In our research, we analysed muscle and different types of fat to understand how body composition can influence the small blood vessels or ‘microcirculation’ of the heart, as well as future risk of heart failure, heart attack and death.”

The new research included 669 people who were being evaluated for chest pain and/or shortness of breath and found to have no evidence of obstructive coronary artery disease. The patients had an average age of 63. The majority (70%) were female and almost half (46%) were non-white.

All the patients were tested with cardiac positron emission tomography/computed tomography (PET/CT) and CT scans.

To quantify the amount of fat stored in muscles, researchers calculated the ratio of intermuscular fat to total muscle plus fat, a measurement they called the fatty muscle fraction.

Patients were followed up for six years and researchers recorded whether any patients died or were hospitalised for a heart attack or heart failure.

People with higher amounts of fat stored in their muscles were more likely to have damage to the blood vessels that serve the heart (coronary microvascular dysfunction or CMD), and they were more likely to go on to die or be hospitalised for heart disease. 

For every 1% increase in fatty muscle fraction, there was a 2% increase in the risk of CMD and a 7% increased risk of future serious heart disease, regardless of other known risk factors and body mass index.

People who had high levels of intermuscular fat and evidence of CMD were at an especially high risk of death, heart attack and heart failure. In contrast, people with higher amounts of lean muscle had a lower risk. Fat stored under the skin (subcutaneous fat) did not increase the risk.