Apparently your muscle mass can predict how long you live.

One of the classes I am in is simply.. Lifespan. We talk about learning theories, ailments that have an impact on your entire life (like cerebral palsy, for example), body systems and how they’re affected by aging (hearing, vision, etc.), how to treat, and maybe more importantly, how to prevent.

One of our class assignments was to read and discuss an article that pertained mostly to the geriatric population. The article we chose was “Muscle Mass Index As a Predictor of Longevity in Older Adults” which was found in The American Journal of Medicine, 127(6), 547-553 and written by Srikanthan, P., & Karlamangla, A. S. Below is a summary of the article which was written by my colleague, Joe. (If you skip down to the colored text, it tells you the important stuff).

“The study authors attempted to determine if muscle mass index (total muscle mass divided by height squared) is a predictor of lower all-cause mortality in older adults.  Body mass index (BMI) has been shown to have inconsistent associations with mortality in older adults.  Total body mass (used in BMI) includes both adipose and muscle tissue, which have different metabolic effects.  Aging is also associated with a changing balance between adipose and muscle tissue.  Therefore, the study authors built off of previous studies showing an inverse correlation between muscle strength and mortality risk in older adults and proposed muscle mass index as a better predictor of mortality than BMI in the elderly.

The Third National Health and Nutrition Examination Survey (NHANES III) was the source of data for the study.  Men 55 years and older and women 65 years and older were included in the study.  Individuals who were underweight, undernourished, or died within 2 years of the NHANES examination were excluded.  Of the 4321 eligible participants identified, 662 were excluded for not having bioelectrical impedance measurements taken during the survey due to contraindications.  Total skeletal muscle mass was calculated using the bioelectrical impedance data.  Mortality for participants was assessed through December 2004 using data from the National Center for Health Statistics Research Data Center.  Other variables in the analysis included age, race, cancer, smoking, insulin resistance, and cardiovascular markers.

Comparing the lowest quartile with the highest quartile muscle mass index, all-cause mortality risk was significantly lower in the highest quartile by a 30% relative reduction, and mortality rate by a 34%.  The third and fourth quartiles (highest muscle mass index) were also significantly lower than the lower quartile, separate and together.  These trends did not hold for non-muscle mass index showing no significant change between lowest and highest.  The trend for BMI was lower for the highest versus lower quartile, though this result was not significant.  The muscle mass index trends hold even when taking into account cardiovascular risk factors and glucose dysregulation, indicating muscle mass index is an independent indicator of mortality in older adults.  Muscle mass index should be looked at for assessing older adults health instead of BMI.  BMI is useful for describing statistical information of large populations.  However, evidence suggests that it is an ineffective tool for inference to individual health status of older adults.  Further, measuring muscle mass leads to potential exercise interventions to increase muscle in older adults determined at-risk with the muscle mass index.  Strengthening is important for longevity, not just a healthy weight!”

So why is this article important?

  1. A persons BMI (body mass index) is not as useful in assessing older adults as their MMI (muscle mass index).
    1. To learn about and calculate your BMI, click here.
  2. Your MMI can be an effective tool for inference in the health status of older adults.
  3. Knowing your  MMI can lead to exercise interventions to increase strength.
  4. Strength is important for longevity- not just a healthy weight.

Take home message- go gain some muscle mass!

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