[bsgreenb]

Even controlling for exercize wouldn't save this study.. Genetic and environmental factors will correlate with a sit-down lifestyle, confounding any possible conclusions.

You could rule out genetic and family environment factors by comparing identical twins who have different sitting habits. My bet is that a big chunk, if not all, of the effect here could be explained by that. For the remaining "effect", you'd still have the issue of non-family environmental collinearity, though.

Maybe you could find a job where people were randomly assigned to sitting vs. standing tasks. That'd be a nifty little natural experiment

[orofino]

Couldn't the same be said of most medical findings? Should we verify all findings utilizing fully controlled testing on twins?

[bsgreenb]

A twin study is just one form of (natural) experiment. It's common in medicine/epidemiology to perform double-blind trials with placebos, etc. Good medical research utilizes experiments rather than assuming causation from correlation like this study does.

I am a big fan of twin studies, though (my background is in behavior genetics). Take the example of smoking. The most solid demonstration that smoking was bad for your health (aside from maybe the experiments on other mammals) was comparison of twins where one twin smoked and the other didn't.