A glance at any official health bodies advice will show that we are entreated to eat more healthily, take more exercise and reduce stress. Presumably, there is some reasonable evidence that these factors play a relatively significant role in disease formation and response (otherwise, one would presume they would not be within the remit of such organisations).
In what little opportunity I've had to read primary research on medical testing, however (I'm a statistician, not a biologist), I've not come across any attempt at stratification for these factors.
If one is, say, testing the response to a new medicine, presuming these factors will promote recovery in your test subjects, then the apparent efficacy of the medicine might be affected by the distribution of these "lifestyle" factors within your test and control groups.
Similarly, on the other side of the coin, if you are testing the response to a new health threat by epidemiological study, a quoted Odds Ratio of 1.2 might be quite radically different for individuals of different general health, yet (in the studies I've read) there seems to be simply a presumption that the control group and the test group will have a similar spread of lifestyles.
It certainly seems to be a relevant factor in some cases as individuals with a history of smoking are almost always controlled for in such epidemiological studies (especially related to lung conditions), but I have never come across similar treatment of individuals in high stress jobs, eating fewer than 5 fruit and veg per day, taking less than three hours exercise a week etc.
For large effects, these factors would probably be insignificant, but where the effect is small (say a slightly efficacious new treatment, or a low risk environmental contaminant), failure to take account of these factors could theoretically lead to the conclusion that the drug is a slight improvement on what we have, or the threat requires some moderate mitigation, when if fact the drug is virtually ineffective in people who are otherwise unhealthy, or the threat is actually zero to a healthy individual, which would be really important conclusions for public health.
My limited interaction with epidemiological studies was quite a few years ago now, so my question is, have things moved on to start controlling for these factors now we have a better idea of their impact, and more significantly, if they have, have any studies from the past been revised in the light of such controls? Also, does anyone know of any accessible studies on the impact of these factors on epidemiology in general?
To clarify in the light of the close reason. The question is a single one which can be simply answered by anyone involved in epidemiology or researching pathology. Do modern epidemiological studies of disease causal factors control for lifestyle factors, such as diet, obesity, exercise and stress? The answer I'm looking for would come from someone who is either involved in epidemiological research or reads a significant number of epidemiology papers and the would at it's simplest be " Yes, they do" or "No they don't". I'm not sure how much less broad it can get.