I've never really been a fan of epidemiology. The media are forever reporting stories of 'recent findings' - based upon epidemiological research - that this or that food or indulgence is 'bad' for you. Frequently, I have heard people say that they now don't know what to believe any more. This tends to undermine the otherwise positive role that science has in society.
Once on the evening news, I heard that chewing a piece of cheese after every meal was a good defence against tooth decay. This was put down to increased saliva flow and changes in mouth pH. The reporter asked the researcher who had discovered this whether eating cheese didn't pose the risk of increasing one's cholesterol and so might lead to heart disease. The response was little more than (and I paraphrase) 'Ah. Well. We only looked at teeth'. Or, put another way, 'We didn't engage in joined-up thinking'.
As somebody once noted at a scientific conference I attended (in Oxford no less), while it may be true that smoking kills, it is more accurate to say that smoking happens to kill a minority of the people that smoke! That is not to advocate smoking. There is a larger quality of life issue involved than simply numbers killed. Rather, it is a criticism of the way in which its harms are presented to us.
This cartoon rather sums it all up.