My memory is not 100% on this so I could be wrong, but I think I remember my ex telling me about this - she is an epidemiologist i.e. specialising in matters to do with health at the population level. What she said was that the idea that wine was good for you in moderation came from studies that failed to account for the ways in which different alcohol habits are associated with different social classes. If you do a study of 100 people who have 1 glass of wine a day and 100 people who have 1 pint of cider a day, what you've got to remember is that the 100 wine drinkers are (on average) going to be more middle/upper class than the cider drinkers. (Maybe not so much nowadays, but certainly in say the 80s if that's when the misconception dates to.) For various reasons, people with more money live longer - they can afford better food, they live in less polluted neighbourhoods, they tend not to have physically hard or dangerous jobs, etc. So your 100 wine drinkers are going to live longer on average, but it's not because of the wine.