The U shaped curve, ie reduction of mortality in light to moderate drinkers, is only found in study's which lump livelong abstainers, ex drinkers, ex binge drinkers, elderly ex drinkers and sick ex drinkers all into one category.

But when you control for these factors the curve disappears.

Many studies have same thing with smoking. For example, one study found that quiting smoking at 30 was associated with higher rates of early mortality than quitting at 50.

Does that mean smoking longer is beneficial? Of course not. The most probable justification for these results is simply that those quiting at age 30 were much more likely to be previous chainsmokers and/or have had some heath problem causing them to quit so much early

Moderate Alcohol Use and Reduced Mortality Risk: Systematic Error in Prospective Studies and New Hypotheses

Estimates of mortality risk from alcohol are significantly altered by study design and characteristics. Meta-analyses adjusting for these factors find that low-volume alcohol consumption has no net mortality benefit compared with lifetime abstention or occasional drinking. These findings have implications for public policy, the formulation of low-risk drinking guidelines, and future research on alcohol and health.

A substantial progressive decrease in the mortality rates among non-smokers over the past half century (due to prevention and improved treatment of disease) has been wholly outweighed, among cigarette smokers, by a progressive increase in the smoker nu non-smoker death rate ratio due to earlier and more intensive use of cigarettes. Among the men born around 1920, prolonged cigarette smoking from early adult life tripled age specific mortality rates, but cessation at age 50 halved the hazard, and cessation at age 30 avoided almost all of it.

Pooled analysis of all identified studies suggested an association between alcohol use and reduced CHD risk. However, this association was not observed in studies of those age 55 years or younger at baseline, in higher quality studies, or in studies that controlled for heart health. The appearance of cardio-protection among older people may reflect systematic selection biases that accumulate over the life course.

Alcohol's contribution to cancer is underestimated for exactly the same reason that its contribution to cardioprotection is overestimated

Alcohol—a universal preventive agent? A critical analysis. The evidence for the harmful effects of alcohol is undoubtedly stronger than the evidence for beneficial effects.

A sophisticated campaign by global alcohol corporations has promoted them as good corporate citizens and framed arguments with a focus on drinkers rather than the supply of alcohol. This has contributed to acceptance in the global governance arena dealing with policy development and implementation to an extent which is very different from tobacco. This approach, which obscures the contribution supply and marketing make to alcohol-related harm, has also contributed to failure by governments to adopt effective supply-side policies.