WHAT SHOULD I TRACK- BMC OR BMD?

In a recent blog, I mentioned that Dexalytics can be used to track an athlete’s bone mineral density (BMD) and/or bone mineral content (BMC). Many readers ask me which is better to track, BMD or BMC? Before I answer that question, it is important to understand these two variables.

 

BMC is a measurement of bone mineral found in a specific area and is measured in grams (g).  BMC can be measured in a specific location (i.e., arm, leg, etc.) or for the total body.

 

BMD, on the other hand, is the amount of bone mineral in bone tissue. It is derived by dividing the BMC (g) by the area (cm2).  BMD is expressed as grams per centimeter squared (g/cm2).  BMD can be measured in a specific region (i.e., arm, leg, etc.) or the total body. Typically, BMD is used in clinical medicine as an indicator of how likely you are to have an osteoporotic fracture.   

 

What’s the difference? While BMC and BMD sound like the same thing, they are really two different measurements of bone.  For example, two athletes who weigh the same may have identical BMC values for their total body or for a particular region but the shorter athlete may have a higher total BMD when compared to the taller athlete at the same weight.  While a very low BMD doesn’t predict a fracture, it may indicate the athlete is at a greater risk for a fracture.

 

What you should know about T and Z-Scores. Important things to know about DXA reports. The T-Score compares an individual’s BMD to an average healthy 30-year old at the peak of their bone mass. On the other hand, the Z-Score for BMD compares an individual’s BMD to an age-matched individual of the same sex and ethnicity.  Both values are listed as the number of standard deviations that individual is away from those comparison values. Typically, a Z-Score of less than –2.0 standard deviations would indicate that an individual has low bone density that would be expected for their age.   

 

Which bone measurement (BMC or BMD) should you track?  BMD may be the better of the two bone measurements for predicting risk of fracture. BMD T-Scores and Z-Scores allow you to compare your athlete’s bone mineral density to a large database and track your athlete.

 

About the Author: Donald Dengel, Ph.D., is a Professor in the School of Kinesiology at the University of Minnesota and is a co-founder of Dexalytics. He serves as the Director of the Laboratory of Integrative Human Physiology, which provides clinical vascular, metabolic, exercise and body composition testing for researchers across the University of Minnesota.

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