Thursday, September 8, 2011

Cardio May Be Killing You

One of the most cherished beliefs in modern medicine, and one of the foundations of every corporate wellness program I've ever heard of, is that aerobic exercise - what most of us call cardio - is essential to health, and the more the better.  Ever since Dr. Kenneth Cooper's work on aerobics in the 1960s, cardio has been the standard recommendation.  In the 1970s, when I first started running, there was a highly publicized study that said no marathon runner had ever had a heart attack. They concluded that marathon running made you immune to heart attacks. This was bullcrap - it was pure selection bias.  When this study was done, marathon running was an obscure sport, and only a few really dedicated people ran marathons, so they were a self-selected group of very unusual people.  As the running fad spread, more and more people, with their checkered pasts, started running, and it wasn't too long before marathon runners started having heart attacks, too.

Over the course of the last few months, prompted by reading Gary Taube's "Why We Get Fat and What To Do About It", I've been going down the rabbit hole of reading tons on "alternate" nutrition, and especially the movement toward paleo dieting: an attempt to eat in ways we seem the best adapted to.  While poking around, I found this remarkable article, Cardio May Cause Heart Disease by Dr. Kurt Harris, M.D., a radiologist. It's long, and based on some preliminary evidence, but really worth reading, if you want all the details. 

The study, published in the journal Radiology in 2009, by Brueckmann and Mohlenkamp et al, is a study of a type of diagnostic imaging called Late Gadolinium Enhancement, one of the new ways to do radiographic imaging to determine if you might have damage to your heart.  Harris goes into a lot of detail on the technique and what it sees, (he is a radiologist, after all), but the important part is that in two groups (admittedly small at 100 people each): one that ran at least 3 marathons a year, and were not diagnosed with diabetes or heart disease, and another group of 100 controls who were not runners, and pretty sedentary.  Many of the control group smoked, too.  What they found was that the marathon runners, while lower in BMI, and (of course) fitter, had more signs of silent (asymptomatic) heart attacks, and damage to their hearts.  Runners had more of the typical patterns for silent heart attack damage, and a second, non-typical kind of heart attack then the sedentary people.  Because the group was small, the statistics didn't say this was significant, but it was close to the usual limit (in fact, I think it was a better association than the first second-hand smoke studies that caused the law-making).

Since most people have limited amounts of time, let me pull some summaries for you from Dr. Harris' piece: 
...I still find no grounds at all to believe that high levels of "cardio" protects your heart or makes you live longer. Certainly not "the more the better" which is what we've been led to think since the 1970s running craze.

I think a modicum of repetitive, aerobic-type physical activity can definitely improve your mood. I like to a run about 5 k a few times a week. It feels good and cross-country seems good for your coordination with all the varied terrain. A little cross-country and some sprinting sure seems to make me more functional.

I am not under the delusion that it will dramatically improve my overall health or my longevity, though. And I've seen no evidence that doing it every day or doing 5 times the mileage would be better. Just the opposite, in fact.

Same goes for eating "fruits and vegetables", gorilla levels of fiber, "antioxidants", and most supplements. No magic foods.

The really good kind of exercise, resistance training, makes you more functional and stronger. That is the only sensible definition of fitness if we follow the hippocratic oath with our selves.
Fitness and strength are good.  Cardio may be good to help prepare for the zombie apocalypse, but don't get hung up on it.


  1. Awesome post. Dr. Harris is one of the folks at the heart of the 'paleo' movement. Been reading him for a while now.

    Small world...

  2. This is a good opportunity to let you know that we've gone mostly Paleo too. I do sprint intervals once a week and we take walks when we can. If you like I'll link my wife's food blog.

  3. Xenocles - yes, please put up a link, or mail it to me (address down the right sidebar)

  4. We are not ashamed to blogwhore, but I prefer to do it with permission.