Despite the various and severe health risks that come with drinking, abstaining from alcohol appears to increase your risk of dying prematurely. The reasons for this are not clearly known, but it is thought to be because drinkers are more likely to belong to a community (albeit one that drinks), and a feeling of community is strongly correlated with happiness and longevity.
Even after controlling for nearly all imaginable variables — socioeconomic status, level of physical activity, number of close friends, quality of social support and so on — the researchers […] found that over a 20-year period, mortality rates were highest for those who were not current drinkers, regardless of whether they used to be alcoholics, second highest for heavy drinkers and lowest for moderate drinkers. […]
These are remarkable statistics. Even though heavy drinking is associated with higher risk for cirrhosis and several types of cancer (particularly cancers in the mouth and esophagus), heavy drinkers are less likely to die than people who don’t drink, even if they never had a problem with alcohol. One important reason is that alcohol lubricates so many social interactions, and social interactions are vital for maintaining mental and physical health. […]
The authors of the new paper are careful to note that even if drinking is associated with longer life, it can be dangerous: it can impair your memory severely and it can lead to nonlethal falls and other mishaps […] that can screw up your life. There’s also the dependency issue.
The correlations between alcohol intake and various health outcomes (both positive and negative) is confusing and varied. A few things seem to be for sure: it can be good and it can be bad; no causation has been proven; and the effects differ between the sexes.
Update: I forgot to link to the published study (Holahan et al., 2010)… the Results section is the one worth perusing. For those without full access to the study (ahem), Overcoming Bias provides the full list of controls.
Update: Jonah Lehrer discusses this study in an article titled Why Alcohol Is Good for You, emphasising the social side of drinking as the key to longevity.