Have the Benefits of Exercise Been Oversold?

One of the things I find interesting about this story, and about other health stories in general, is that it's hard to isolate exactly which behaviors are affecting which health benefits. A person is healthier if they don't smoke, for instance, but are they a sedentary non-smoker or an active non-smoker? Here's a couple of graphs that talk about this:

"Active people are much less likely to smoke; they’re thinner and they eat differently than their sedentary peers. They also tend to be more educated, and education is one of the strongest predictors of good health in general and a longer life. As a result, it is impossible to know with confidence whether exercise prevents heart disease or whether people who are less likely to get heart disease are also more likely to be exercising.

"Scientists have much the same problem evaluating exercise and cancer. The same sort of studies that were done for heart disease find that people who exercised had lower rates of colon and breast cancer. But whether that result is cause or effect is not well established."

I don't think the article means to say that exercise itself is any less good for us than we thought. I think the emphasis is more that no one single thing can be isolated as a cure-all (which we know, but we keep looking for it anyway!) I think a person who exercises will, naturally, seek other healthful ways of living; and that a person who eats well may naturally seek exercise; and then that person will decide that smoking is not good for their body, or that they need to cut down on sugar and white foods, or that they need to drink more water. Maybe we can think of exercise as the trunk of the tree, while acknowledging that other branches are really important to the system as well.