Muscle Mass Predicts Longevity Better Than BMI

I'm on record stating that BMI is a crock.  I arrived at that conclusion through reasoning, not scientific research.  But now there is scientific research that demonstrates that BMI is a poor predictor of longevity, and that muscle mass is a better predictor of longevity.

Doctors routinely measure a patient's body mass index, or BMI. And if that weight-to-height ratio points to obesity, the doc might prescribe exercise, to shed the extra pounds. But when it comes to longevity, a focus on weight loss may be misplaced. Because BMI isn't actually a very reliable indicator of life span. A more useful measure, some physicians say, might be muscle mass. 

Researchers analyzed BMI and muscle mass data from more than 3,600 seniors in a long-term study. And they tracked which seniors had died, a decade later. Turns out BMI wasn't much good at predicting chance of death.

But muscle mass was: more muscle meant better odds of survival. The study appears in The American Journal of Medicine. [Preethi Srikanthan and Arun S. Karlamangla, Muscle Mass Index as a Predictor of Longevity in Older-Adults]

From the abstract:

Objective
Obesity (as defined by body mass index) has not been associated consistently with higher mortality in older adults. However, total body mass includes fat and muscle, which have different metabolic effects. This study was designed to test the hypothesis that greater muscle mass in older adults is associated with lower all-cause mortality. 

Methods
All-cause mortality was analyzed by the year 2004 in 3659 participants from the National Health and Nutrition Examination Survey III who were aged 55 years or more (65 years if women) at the time of the survey (1988-1994). Individuals who were underweight or died in the first 2 years of follow-up were excluded to remove frail elders from the sample. Skeletal muscle mass was measured using bioelectrical impedance, and muscle mass index was defined as muscle mass divided by height squared. Modified Poisson regression and proportional hazards regression were used to examine the relationship of muscle mass index with all-cause mortality risk and rate, respectively, adjusted for central obesity (waist hip ratio) and other significant covariates. 

Results
In adjusted analyses, total mortality was significantly lower in the fourth quartile of muscle mass index compared with the first quartile: adjusted risk ratio 0.81 (95% confidence interval, 0.71-0.91) and adjusted hazard ratio 0.80 (95% confidence interval, 0.66-0.97). 

Conclusions
This study demonstrates the survival predication ability of relative muscle mass and highlights the need to look beyond total body mass in assessing the health of older adults.

I probably shouldn't have read the comments to the Scientific American article, but I did, and they are sadly typical of the kind of ignorance, laziness and plain stupidity one encounters on the internet.

Jerzy v. 3.0. March 21, 2014, 7:23 AM
Low muscle mass in elderly people may mean that all their systems are falling already. Questionnaire about exercise might be more meaningful. Correlation doesn't imply causation, sorry.

jtdwyer to Jerzy v. 3.0. March 21, 2014, 7:34 AM
Exactly! What's most important here is that BMI is a (loosely) quantifiable indicator of lifestyle health for children and young adults - for whom lifestyle factors contribute most greatly to long term health and survival.
Unfortunately, increasing muscle mass in the elderly is not likely to reduce morbidity! 

The responders obviously didn't read the abstract, because the answer to their objection about frailty in old age, near death is right there where I highlighted it in bold.  The researchers measured the subjects' muscle mass index when they were 55 (men) or 65 (women) years old between 1988 and 1994, not when they died.  They analyzed the causes of mortality in 2004.  They also eliminated all subjects who were underweight in the first two years after the survey to eliminate individuals whose "systems are failing already".

Worse still, the responders obviously didn't even bother to read the article to which they responded.

There's no cause-and-effect here—just correlation for now. But study author Preethi Srikanthan, of U.C.L.A., has this recommendation: "Get up and start moving. Focus on trying to maintain the maximum amount of resistance training that you can, and stop worrying so much about dropping calories." Which could take a little weight off your mind, too.

Jeeze.

Anyway, Dr Srikanthan's advice isn't all that helpful.  How exactly does one "get up and start moving" and "focus on trying to maintain the maximum amount of resistance training that you can"?

People gain muscle and strength most easily in their teens, twenties and thirties.  After that, a person's hormone profile makes it increasingly more difficult.  The solution then, is to increase ones muscle mass as much as healthfully possible while young and maintain it as much as possible as one ages.  But how?  And what if one is already past 50?  Is it too late?

One shouldn't expect a physician to have the answer (it's not their specialty) and Dr Srikanthan doesn't, but that's OK, because Mark Rippetoe does.

Strength — as well as a tolerance for childish nonsense — is the thing we all lose as we age. Squatting down, standing back up, putting things overhead, pulling things up the driveway, loading the groceries, wrestling with the grandkids, teaching the dog who’s boss, mowing the yard, putting the broken lawnmower in the truck again: simple physical tasks we took for granted years ago are often problems for older, weaker people, as well as a source of potential injury that can be expensive and debilitating. 

Source: PJ Media

For most of us, this happens because of inactivity. If you do not use your muscles to produce enough force to maintain their ability to do so, it shouldn’t be surprising that they become less capable of doing it. And walking, running, riding a bicycle — physical activities whose performance is not limited by strength for even moderately active people — cannot increase or even maintain strength.

So, how does one fix this problem?

The absence of skeletal loading is typical for older people, since we now hire the heavy work done instead of doing it ourselves. And just like muscles, bones adapt to the “stress” of being unloaded by getting thinner and less dense. Running is not a weight-bearing exercise in the sense that strength training is. It’s just a “you-bearing” exercise, and the impact of repeated footfalls affects only the legs. In fact, people sensitive to impact have far fewer problems with the static nature of barbell training than they do the repeated impacts of running. A barbell sitting on the shoulders or held overhead in the hands loads the skeleton in a way that other exercises cannot do, and a strength training program always results in the preservation of bone density. Coupled with the strength necessary to control your balance, this is the best insurance against the tragic and often fatal pelvic fracture that an older person can acquire. 

Source: PJ Media

But the loss of strength can be slowed down quite a bit, and for older people who have never trained before, a vast amount of improvement can take place in a relatively short span of time. I have trained many older competitive “masters” lifters who started out as disinterested gym members and then experienced a sudden change of attitude when their strength doubled with six months of lifting weights. These people will tell you about the difference strength training — not running — has made in their lives. 

Here's a quote from the 3rd edition of Starting Strength: Basic Barbell Training.

Weight training is precisely scalable to the age and ability of the individual lifter... We have 11-pound bars - or even broomsticks - for kids to start lifting with... This logic also applies to every group of people who might be viewed as a "special population" - the frail elderly, people with skeletal and muscular disease, the completely sedentary, the morbidly obese... In fact, the adaptation to weight training is precisely the adaptation that these special populations need... (pages 322-323)

For further details, read the rest of Rippetoe's articles on PJ Media, then get the book.

Finally, the subject of BMI reminded me of this.

My life insurance policy went up $98 a month after my BMI was checked. Blood work, body fat, overall fitness.....not important. @CrossFit
— Jason Khalipa (@JasonKhalipa) December 14, 2013

This is Jason Khalipa.

Jason Khalipa BMI = 31 (obese)

See what I mean?  BMI is a crock.