The Financial Times recently ran an article about Jerry Morris, a London epidemiologist who did the most famous study of the effect of exercise. He compared London bus drivers with the ticket takers on the same buses. The ticket takers got a lot more exercise than the drivers. The health differences between them were attributed to exercise:
â€œThere was a striking difference in the heart-attack rate. The drivers of these double-decker buses had substantially more, age for age, than the conductors [= ticket takers].â€ [said Morris]
The data were so telling because drivers and conductors were men of much the same social class. There was only one obvious difference between them. “The drivers were prototypically sedentary,” explains Morris, “and the conductors were unavoidably active. We spent many hours sitting on the buses watching the number of stairs they climbed.” The conductors ascended and descended 500 to 750 steps per working day. And they were half as likely as the drivers to drop dead of a sudden heart attack.
Morris found that bus conductors had fewer heart attacks than sedentary drivers
Today, almost everyone understands that physical exercise can help prevent heart disease, as well as cancer, diabetes, depression and much else besides. But on that day in 1949 when Morris looked at the bus data, he was the first person to see the link. He had inadvertently — “mainly luck!” — “ stumbled on a great truth about health: exercise helps you live longer.
It’s not that simple. There are two big confounds in the study (two other differences between drivers and ticket takers) that surely caused Morris to overestimate the benefits of exercise. One is well-known to epidemiologists: Bus driving is very stressful. Much more stressful than a dozen other equally sedentary jobs. Stress certainly causes heart disease. The other is based on my discovery that standing a lot improves sleep. (The standing needn’t involve movement.) I don’t know if better sleep specifically reduces heart disease but it certainly increases resistance to infection and heart disease seems to have an infectious component. The ticket takers were on their feet all day, the drivers were not.
You may remember that James Fixx, a famous advocate of jogging, died of a heart attack.
Thanks to Dave Lull.