Oh Well
From the NYTimes

By now, it is a familiar litany. Study after study suggests that alcohol in moderation may promote heart health and even ward off diabetes and dementia. The evidence is so plentiful that some experts consider moderate drinking — about one drink a day for women, about two for men — a central component of a healthy lifestyle.

But what if it’s all a big mistake?

For some scientists, the question will not go away. No study, these critics say, has ever proved a causal relationship between moderate drinking and lower risk of death — only that the two often go together. It may be that moderate drinking is just something healthy people tend to do, not something that makes people healthy.

“The moderate drinkers tend to do everything right — they exercise, they don’t smoke, they eat right and they drink moderately,” said Kaye Middleton Fillmore, a retired sociologist from the University of California, San Francisco, who has criticized the research. “It’s very hard to disentangle all of that, and that’s a real problem.”

I always figured that by the time you found people who are disciplined enough to drink every day - but only ever 2 - you've got people disciplined enough to make lots of other healthy decision. But I never really thought through the ethical and practical problems in running a test thorough enough to settle the matter. The interesting bits of this article get into those difficulties.