Throughout the 10,000 or so years that humans have been drinking fermented beverages, they've also been arguing about their merits and demerits. The debate still simmers today, with a lively back-and-forth over whether alcohol is good for you or bad for you.

It's safe to say that alcohol is both a tonic and a poison. The difference lies mostly in the dose. Moderate drinking seems to be good for the heart and circulatory system, and probably protects against type 2 diabetes and gallstones. Heavy drinking is a major cause of preventable death in most countries. In the U.S., alcohol is implicated in about half of fatal traffic accidents.(1) Heavy drinking can damage the liver and heart, harm an unborn child, increase the chances of developing breast and some other cancers, contribute to depression and violence, and interfere with relationships.

Alcohol's two-faced nature shouldn't come as a surprise. The active ingredient in alcoholic beverages, a simple molecule called ethanol, affects the body in many different ways. It directly influences the stomach, brain, heart, gallbladder, and liver. It affects levels of lipids (cholesterol and triglycerides) and insulin in the blood, as well as inflammation and coagulation. It also alters mood, concentration, and coordination.

Loose use of terms has fueled some of the ongoing debate about alcohol's impact on health. In some studies, the term "moderate drinking" refers to less than one drink per day, while in others it means three or four drinks per day. Exactly what constitutes "a drink" is also fairly fluid. In fact, even among alcohol researchers, there's no universally accepted standard drink definition.(2)

In the U.S., one drink is usually considered to be 12 ounces of beer, 5 ounces of wine, or 1½ ounces of spirits (hard liquor such as gin or whiskey).(3) Each delivers about 12 to 14 grams of alcohol.

The definition of moderate drinking is something of a balancing act. Moderate drinking sits at the point at which the health benefits of alcohol clearly outweigh the risks. The latest consensus places this point at no more than one to two drinks per day for men, and no more than one drink per day for women. This is the definition used by the U.S. Department of Agriculture and the Dietary Guidelines for Americans, and is widely used in the U.S.

More than 100 prospective studies show an inverse association between moderate drinking and risk of heart attack, ischemic (clot-caused) stroke, peripheral vascular disease, sudden cardiac death, and death from all cardiovascular causes.(4) The effect is fairly consistent, corresponding to a 25-40% reduction in risk.

The connection between moderate drinking and lower risk of cardiovascular disease has been observed in men and women. It applies to people who do not apparently have heart disease. It also applies to those at high risk for having a heart attack or stroke or dying of cardiovascular disease - people with type 2 diabetes and those with high blood pressure, angina (chest pain), a prior heart attack, or other forms of cardiovascular disease.

The idea that moderate drinking protects against cardiovascular disease is biologically and scientifically plausible. Moderate amounts of alcohol raise levels of high-density lipoprotein (HDL, or "good" cholesterol), and higher HDL levels are associated with greater protection against heart disease. Moderate alcohol consumption has also been linked with beneficial changes in a variety of factors that influence blood clotting, such as tissue type plasminogen activator, fibrinogen, clotting factor VII, and von Willebrand factor.(6) Such changes would tend to prevent the formation of small blood clots that can block arteries in the heart, neck, and brain, the ultimate cause of many heart attacks and the most common kind of stroke.

Learn more at: http://www.hsph.harvard.edu/nutritionsource/alcohol.html