As most people know, just because two things occur together does not mean that one caused the other. Correlation and causality are two different things. It is important to keep this in mind when reading about human health studies in the news. Epidemiology is a wonderful tool however, and provides clues to problems that might have gone unnoticed. In addition to identifying potential problems correlational (and epidemiological) studies are important in evaluating how a problem identified in the lab may be harming people in the real world. Are light drinkers more likely to eat better, exercise better, be healthier than those who drink more alcohol or even none at all?
An important next step is figuring out why the correlation exists. A good explanation of what is going on was published by He et al. (2007) and was supported by their lab studies. Light alcohol intake activates a beneficial biochemical pathway. The end result is that the body is better able to synthesize glycogen, removing glucose from the bloodstream. Higher alcohol intake disrupts glucose metabolism by activating an additional protein that blocks the positive effects seen with light alcohol intake. This is a very simplified explanation, but you can think of it as someone suddenly pulling the emergency brake while driving. Doing that long term can inflict some serious damage. Stressing the system that controls your blood sugar over long periods of time can result in diabetes and other health problems.
I’ve had some questions about alcohol consumption and the paleo diet. Some people seem to hold that hard liquor is OK because it is low-carb and is not metabolized in the same manner as beer and wine. Its true that ethanol (alcohol) follows a different path than carbohydrates, but this does not mean it is a good path to follow. Alcohol has been shown to lower production of insulin, which some also favor in the belief that keeping insulin levels low is a goal in itself. Keeping insulin levels low when blood sugar is high is not a good thing to aim for. Its the sugar that is dangerous.
Joosten MM, Chiuve SE, Mukamal KJ, Hu FB, Hendriks HF, & Rimm EB (2011). Changes in alcohol consumption and subsequent risk of type 2 diabetes in men. Diabetes, 60 (1), 74-9 PMID: 20876712
Ajani UA, Hennekens CH, Spelsberg A, & Manson JE (2000). Alcohol consumption and risk of type 2 diabetes mellitus among US male physicians. Archives of internal medicine, 160 (7), 1025-30 PMID: 10761969
He L, Marecki JC, Serrero G, Simmen FA, Ronis MJ, & Badger TM (2007). Dose-dependent effects of alcohol on insulin signaling: partial explanation for biphasic alcohol impact on human health. Molecular endocrinology (Baltimore, Md.), 21 (10), 2541-50 PMID: 17622585
Nguyen KH, Lee JH, & Nyomba BL (2012). Ethanol causes endoplasmic reticulum stress and impairment of insulin secretion in pancreatic β-cells. Alcohol (Fayetteville, N.Y.), 46 (1), 89-99 PMID: 21840159