Muscle Mass & Death From Heart Disease
Title: Relation of Muscle Mass and Fat Mass to Cardiovascular Disease Mortality
Author: Srikanthan et al
Journal: American Journal of Cardiology
Objective: To evaluate the relation between components of body composition and mortality in patients with cardiovascular disease (CVD).
Body mass index is a highly utilized and well documented method for assessing risk of death from many causes, including cardiovascular disease. If you are unfamiliar with BMI, check out my video explaining it.
BMI Explained: https://www.youtube.com/watch?v=LeG45M4XTjA
Body mass index is calculated by dividing your height by your weight squared (in the metric system, in the SI system it’s a little more complicated). This gives you a rough estimate of your body habitus, and a healthy BMI is anywhere between 20 and 25. Anything over 25 and you have increased risk of heart attack among other things.
One of the criticisms of BMI, which is well documented, is that it does not accurately differentiate body fat from body muscle. For example, if you took a 6’2”, 230 lb pro athlete and and 6’2” 230 sedentary individual who doesn’t exercise, they have the same body mass index of 29.5. However, in this thought exercise, the pro athlete will have much more muscle mass and less body fat.
In other words, should people with more muscle mass and less body fat be healthier despite the same body mass index? The authors of this study wanted to shed some light on that question.
They used dual x-ray absorptiometry body composition data from the National Health and Nutrition Examination Survey (1999 to 2004) which they linked to total and CVD mortality data (1999 to 2006) in 6,451 patients with CVD.
Kaplan-Meier survival analysis for the endpoints of total and CVD mortality which was plotted by quartiles of muscle mass, fat mass, and categories of body mass index (BMI).
Subjects were stratified into 4 groups
- low muscle/low fat mass
- low muscle/high fat mass
- high muscle/low fat mass
- high muscle/high fat mass
Surprisingly, rates of cardiovascular and total mortality were lower in higher quartiles of muscle mass, fat mass, and higher categories of BMI (p <0.001).
The high muscle/low fat mass group had a lower risk of CVD and total mortality
- 68% reduction in CVD mortality (HR 0.32, 95% CI 0.14, 0.73)
- 62% reduction in Total mortality (HR 0.38, 95% CI 0.22, 0.68)
Thus, increasing fat mass, muscle mass, and BMI were all correlated with improved survival.
The specific subgroup of high muscle and low fat mass had the lowest mortality risk compared with other body composition subtypes.
Rather than exclusively leaning on the BMI to assess cardiovascular disease risk, this study reinforces the importance of body composition in determining risk.
Interestingly, high fat, high muscle individuals in the higher BMI range had improved survival compared to low muscle and low fat groups as well as individuals in the lower tier of BMI.
To me, this signifies the importance of lean skeletal muscle and fitness in determining and reducing your risk of cardiovascular and total mortality.
Srikanthan, P., Horwich, T. B., & Tseng, C. H. (2016). Relation of Muscle Mass and Fat Mass to Cardiovascular Disease Mortality. The American Journal of Cardiology, 117(8), 1355-1360. doi:10.1016/j.amjcard.2016.01.033