How much does exercise affect health?

Posted by Dave on April 2, 2010 | 3 Comments

In 1966, a team led by Jerry Morris published a groundbreaking study on London bus drivers and conductors. The drivers sat in seats day in and day out, basically completely sedentary. Conductors were constantly on the move, traveling up and down the stairs and back and forth to collect fares. So did these different behaviors in otherwise similar jobs have any effect on health? This chart sums up the results:

Conductors were significantly less likely to experience ischaemic heart disease than drivers. The difference was especially pronounced at younger ages. Drivers in their forties were nearly five times more likely to get heart disease than conductors. Incidence was as high in 40-ish drivers as it was in 60-ish conductors!

While it’s not necessarily true that inactivity was completely to blame for the discrepancy — perhaps driving is more stressful than conducting — it’s a powerful demonstration that a sedentary lifestyle can have a large impact on health.

Liam Donaldson, the Chief Medical Officer of England, highlights the relationship between physical activity and health in his latest annual report.

The report claims that physical inactivity is more widespread than smoking, obesity, and alcohol abuse, and costs the English economy and health service nearly £10 billion per year. The table below summarizes the claims:

I’m always a little skeptical of claims like this — aren’t all these things related? If I’m more active, I might miss less work because of health reasons, but I also might not be as productive because the exercise itself is wearing me out. If I start running regularly, I might be inclined to quit smoking too. And maybe I’d lose some weight, which would diminish obesity-related problems.

And then there are those troubling reports like the one I mentioned yesterday, suggesting that a little exercise doesn’t compensate for a generally sedentary life. Can 30 minutes of exercise a day really ever compensate for that? It more exercise is required, who has the time to manage it?

The Chief Medical Officer’s report also claims that physical activity can reduce disease:

Again, its unclear how confident the Chief Medical Officer is in these conclusions. I’d like to take a closer look at some of the reports that are cited here to get a better sense of the impact of physical activity. Note too that the activity levels in this chart vary. If “most active” individuals have a 40 to 50 percent lower risk of colon cancer, how much does a moderate level of activity help? Does it help at all? What’s the ideal level of activity? Is it viable for someone like me who sits at a desk all day?

I’ll try to answer some of these questions next week. Meanwhile, don’t forget to check out my food and exercise record. I lost two pounds today — will I gain it back over Easter weekend?

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