Friday, June 22, 2012

A treasure trove

Since I started training for my first half-marathon, I have come to love running.  I always knew I might, but never stuck at it long enough to find out.  With my race less than 2 months away, I'm about at the half way mark of training.  Things have been going well enough that I plan on continuing to long-distance run and aim for longer average distances over time.

Being a medical science nerd, I was interested to find out what exactly the health benefits of long distance running are, since people invariably point to the reported cases of deaths during marathons every year.  I assumed this must be a case of recall bias, that being that things which you've read frequently or can easily recall seem more common than they really are.  But where to find the data to support it?  Turns out, I'm not the only one who wants an answer to this question.

Paul Williams, a researcher at Lawrence Berkeley National Laboratory, has published TONS of data from his National Runners' Health Study.  I just searched his name on Pubmed and came across the following data supporting the health benefits of long-distance running.

1.  Risk for stroke is substantially reduced in those who exceed recommended physical activity levels, even after controlling for consequent reduction in blood pressure, diabetes, cholesterol, and body weight.
2.  Higher fitness levels reduce the odds of high blood pressure, high cholesterol, and diabetes.
3.  Risk of high cholesterol declines in step with increasing average running distance.
4.  Incidence of diabetes declines significantly with increasing average weekly running distance, even when adjusted for age and body mass index.
5.  Of interest, although many assume that fitness leads to weight loss, study after study after study has failed to prove this association.  One of the National Runners' Health Study reports shows that pre-study BMI accounted almost entirely for the association between BMI and fitness levels.  That is, those who are already lean are more likely to be faster runners and run more often and, not surprisingly, have the lowest BMIs at the end of the study as well.  So the association between fitness and body weight can be almost entirely explained by ones existing body weight.  Meaning that it is correlational and not causative as many would assume.
6.  While consistent long distance running does not seem to promote weight loss, it does seem to protect against the weight gaining effects of North American diets.  So it may not make you lose weight, but it will prevent you from gaining.
7.  An interesting study looked at active vs. non-active monozygotic twins.  It showed that vigorous physical activity attenuated the genetic "risk" of obesity.  Meaning that whatever genetic component contributes to obesity risk and body weight, it should be equal in identical twins.  So if one is a long distance runner and the other is not, and the active one has a lower BMI than the sedentary one, you can assume it is the running helping out the situation (they controlled for cigarette use, diet, education, etc.)
8.  Just in case the news stories still have you worried, take it from André Picard, the best health reporter in Canada.  From his article, you find out the following:
Donald Redelmeier, a professor of medicine at the University of Toronto, examined records from marathons where there were 3.3 million participants over a 30-year period. There were 26 deaths. That’s a death rate of one in 126,000 – roughly the same as the death rate in the general population. Stated plainly, people die of heart disease, not running.
9.  And, in case you are still not convinced, this study conclusively shows that despite a massive increase in marathon participation in the last 30 years, deaths on the course have not become more common and continue to be rare.  

So, here I am, happy with my decision to pursue a recreational activity that I not only enjoy but that has myriad health benefits.

(As an aside, although the plural of "anecdote" is not "proof" I am certainly the embodiment of science's failure to find a weight loss effect of exercise.  Since April 30, I have run almost 100 miles, averaging 13 miles per week.  I have gained almost 5 pounds in that time.  Boo!)

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