Higher Aerobic Fitness at Any Weight Associated with Decreased Mortality

[Dean Pomerleau]

All,

 

There is a new study [1] out this week getting lots of media attention with headlines like Study: Obesity more dangerous to health than lack of fitness and 'Fat but fit' counts for nothing scientists say.

 

After reading the full text (via sci-hub.io) it appears this is a gross oversimplification, if not outright distortion of what the study really says. In the study, researchers looked at the aerobic fitness and weight of 1.3 million Swedish men at the time of their military conscription (mean age 18). Aerobic fitness was tested by seeing how long the men could keep pedalling on a stationary bike whose resistance was increased at a rate of 2.5 watts/min. The subjects were then followed for an average of 29 years (to around age 47 - so still relatively young), during which 44K of them died. They then compiled statistics about mortality rate as a function of both baseline weight and baseline aerobic fitness.

 

The results of the entire study are nicely summarized in a single graph (don't you love it when that happens?!). Here it is:

 

 

There are several interesting things that can be gleaned from this graph:

• Being more aerobically fit resulted in reduced mortality across all four BMI categories.
• There was virtually no difference in the mortality rate of men with low BMI (< 18.5) vs. normal BMI (18.5 - 25). The fact that the researchers did not correct for smoking would seem to make this lack of difference even more significant, since it is likely that the skinny group smoked more than the normal weight group, and so would be expected to have a higher mortality rate, based on many other studies.
• The most fit obese men were significantly more likely to die than the least fit normal or even overweight individuals. 

It is only the last of these three points which seem to have sparked all the media attention. But as you can see, the study has much more interesting information than just that, particularly for us CR practitioners - namely that when it comes to reducing mid-life mortality, being skinny isn't bad and being more aerobically fit is good.

 

--Dean

 

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[1] International Journal of Epidemiology, 2015, 1–10 doi: 10.1093/ije/dyv321

 

Aerobic fitness in late adolescence and the risk

of early death: a prospective cohort study of 1.3

million Swedish men

 

Gabriel Hogstrom, Anna Nordstrom and Peter Nordstrom

 

Full text (via sci-hub.io): http://ije.oxfordjournals.org.sci-hub.io/content/early/2015/12/20/ije.dyv321.full

 

Abstract

Background: Fitness level and obesity have been associated with death in older populations.

We investigated the relationship between aerobic fitness in late adolescence and

early death, and whether a high fitness level can compensate the risk of being obese.

Methods: The cohort comprised 1 317 713 Swedish men (mean age, 18 years) that conscripted

between 1969 and 1996. Aerobic fitness was assessed by an electrically braked

cycle test. All-cause and specific causes of death were tracked using national registers.

Multivariable adjusted associations were tested using Cox regression models.

Results: During a mean follow-up period of 29 years, 44 301 subjects died. Individuals in the

highest fifth of aerobic fitness were at lower risk of death from any cause [hazard ratio (HR),

0.49; 95% confidence interval (CI), 0.47–0.51] in comparison with individuals in the lowest

fifth, with the strongest association seen for death related to alcohol and narcotics

abuse (HR, 0.20; 95% CI, 0.15–0.26). Similar risks were found for weight-adjusted aerobic fitness.

Aerobic fitness was associated with a reduced risk of death from any cause in normalweight

and overweight individuals, whereas the benefits were reduced in obese individuals

(P< 0.001 for interaction). Furthermore, unfit normal-weight individuals had 30% lower risk

of death from any cause (HR, 0.70; 95% CI, 0.53–0.92) than did fit obese individuals.

Conclusions: Low aerobic fitness in late adolescence is associated with an increased risk

of early death. Furthermore, the risk of early death was higher in fit obese individuals

than in unfit normal-weight individuals.

 

Key words: Fitness, obesity, death

 

PMID: 26686843

[nicholson]

"The fact that the researchers did not correct for smoking"  .......  nor perhaps for the fact that some of the people with low body weight would have had low body weight because they were already sick, and therefore more likely to die early?

 

Rodney.

 

=======

 

"The unverified conventional wisdom is almost invariably mistaken."

[Dean Pomerleau]

"The fact that the researchers did not correct for smoking" ....... nor perhaps for the fact that some of the people with low body weight would have had low body weight because they were already sick, and therefore more likely to die early?

 

You are right Rodney, rereading the full text I couldn't find any indication that the authors excluded any earlier deaths, meaning the skinniest people may have had a latent disease and artificially pushed up the mortality rate of the thin category of men.

 

But the very young age of the men at baseline (18 years) makes this less of a problem than in other cohorts, since such young men are unlikely to have latent diseases like cancer that caused their thinness.

 

--Dean

[nicholson]

This should have enormous implications for the 'education' system.  Of course it won't.

 

Rodney.

 

==========

 

"The unverified conventional wisdom is almost always mistaken."

[Guest Maddie]

 

"The fact that the researchers did not correct for smoking" ....... nor perhaps for the fact that some of the people with low body weight would have had low body weight because they were already sick, and therefore more likely to die early?

You are right Rodney, rereading the full text I couldn't find any indication that the authors excluded any earlier deaths, meaning the skinniest people may have had a latent disease and artificially pushed up the mortality rate of the thin category of men.

 

But the very young age of the men at baseline (18 years) makes this less of a problem than in other cohorts, since such young men are unlikely to have latent diseases like cancer that caused their thinness.

 

--Dean

 

...except respiratory illnesses.  Such young men are likely to have many respiratory illnesses that would kill them years later and also result in low weight then.  They're also the MOST likely to have hidden drug problems, which is also associated with low weight/high mortality (though as much from external causes as drugs themselves--risk-taking, bad friends, depression, etc.)