[alexey-salmin]

I had a somewhat similar question about exercise vs physically demanding work, since the former helps to have a healthy heart and the latter seems to do the opposite. Explanations I've found were tied to the average daily heart rate. Exercises are intense but it's only a few hours per week, and over time they tend to lower the average heart rate. Physical work is typically less straining but it takes a big portion of the week and as the result increases the average heart rate.

I guess the problem of exercise (intense but short) vs chronic stress (moderate but 24x7) could have a similar explanation.

[mattmaroon]

I would be willing to bet that there are just confounding factors. People who do physical work differ from people who do not in so many ways that it would be impossible to do any sort of controlled study.