A study has revealed a new risk factor for heart disease that transcends traditional measures such as body mass index (BMI). The research, led by Professor Viviany Taqueti, Director of the Cardiac Stress Laboratory at Brigham and Women's Hospital, US, has found that individuals with fat deposits within their muscles are at a higher risk of heart disease, irrespective of their BMI. This discovery could significantly alter our understanding and evaluation of heart disease risk.
The study involved an in-depth analysis of muscle and different types of fat in 669 people. The aim was to understand how body composition can influence the small blood vessels or 'microcirculation' of the heart, as well as the future risk of heart failure, heart attack, and death. The team used CT scans to measure the amounts and location of fat and muscle in a section of the patients' torso, calculating the ratio of intermuscular fat to total muscle plus fat, a measurement they termed the 'fatty muscle fraction'.
The results of the study were revealing. For every 1 per cent increase in fatty muscle fraction, there was a 2 per cent increase in the risk of coronary microvascular dysfunction (CMD) and a 7 per cent increased risk of future serious heart disease. This was regardless of other known risk factors and body mass index. This suggests that traditional measures such as BMI or waist circumference may not be adequate to evaluate the risk of heart disease accurately for all people.
Interestingly, people with higher amounts of lean muscle had a lower risk. Fat stored under the skin (subcutaneous fat) did not increase the risk. Professor Taqueti explained that fat stored in muscles may contribute to inflammation and altered glucose metabolism, leading to insulin resistance and metabolic syndrome. These chronic insults can cause damage to blood vessels, including those that supply the heart, and the heart muscle itself.
The team is now assessing the impact of treatment strategies including exercise, nutrition, weight-loss drugs, or surgery, on body composition and metabolic heart disease, to help lower the risk for people with fatty muscles. These findings could be particularly important for understanding the heart health effects of fat and muscle-modifying incretin-based therapies, including the new class of glucagon-like peptide-1 receptor agonists.
In addition to the primary study, several other relevant studies have been conducted. For instance, a study on the association between waist circumference and the prevalence of hypertension among US adults found that after resting for 5 minutes, certified examiners measured the systolic blood pressure and diastolic blood pressure using a mercury sphygmomanometer. The results showed significant positive associations across all metrics for endometrial and post-menopausal breast cancer in women.
Another study on the impact of body mass index on worsening of diastolic function and impairment of left atrial strain in the general female urban population found that left atrial function measured by phasic two-dimensional strain has shown its importance in diagnosing left ventricular diastolic dysfunction (LVDD), especially in its early stages, and in grading its severity.
