Does Exercise Decrease Risk Of Heart Attack?
I confess that I am not a compulsive reader of obituaries. On the other hand my wife, who is an attorney, picks up our local paper and first turns to the obituary page to find out if any of her clients has died. I guess that’s important for attorneys to know. I did, however, read an obituary published in the New York Times today (Sunday, November 8, 2009). The piece was written by Dennis Hevesi and was entitled “Jeremy Morris, 99 and ½; Proved Exercise Is Heart-Healthy.” Years earlier I had read most of Dr. Morris’s papers but I had completely forgotten about him and his research although what he taught me is firmly implanted in my approach to medical care.
Bus drivers vs. conductors
Dr. Morris was a British epidemiologist who hypothesized in the 1940’s that one could prove that exercise was heart-healthy by studying bus drivers and conductors on London double-decker buses. Drivers spend 90% of their workday sitting down while conductors walked up and down the bus stairs about a million times each day (actually about 600 stairs per day). In a paper published in 1953, Dr. Morris showed that heart attack rates were dramatically lower in the conductors. Follow-up studies showed that although the conductors, on average weighed less than the drivers, the rates were not closely related to weight or body type, including waist size. He later studied postal workers, clerks and telephone operators vs. those who delivered the mail by walking or by bicycling. The delivers had much lower risks of heart attack. The strongest proof for the relationship between physical activity and risk for heart attack came from studies Dr. Morris conducted in the 1960s. He looked at heart attack risks in a large group of men with sedentary government jobs in relation to their degree of aerobic activities outside work. He found that those who performed vigorous exercise on a regular basis had a 50% risk reduction for heart attack. The importance of Dr. Morris’s studies cannot be overemphasized. In my opinion, most of what we now know about exercise and cardiovascular health was the direct result of his ground-breaking work.
The limitations of epidemiologic studies
Not to diminish the importance of Dr. Morris’s work, I need to remind you that epidemiologic studies cannot prove cause and effect but only show relationships. For example, maybe bus drivers, postal clerks, and office workers are under more stress than bus conductors and postal delivery personnel? And maybe people who have sedentary government jobs and who don’t exercise regularly just have different personality types (e.g., ‘type A” vs whatever) than those who do exercise regularly and that is the reason for the study findings? Anyway, it’s a pretty good bet that it’s the exercise per see that lowers the heart attack risk. By the way, it may just be a fluke but Dr. Morris exercised regularly his whole life and lived to 99 and ½ and didn’t die of heart disease.
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