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WHO EXPERT COMMITTEE ON PROBLEMS RELATED TO ALCOHOL CONSUMPTION, 2007
http://www.who.int/entity/substance_...hol_trs944.pdf

2.4 Toxic effects of alcohol
Alcohol is a toxic substance related to more than 60 different disorders.
For some chronic health conditions in which alcohol is implicated, such as breast cancer among women, there is an increasing risk with increasing levels of alcohol consumption, with no evidence of a threshold effect.
For some other conditions, such as liver cirrhosis, the risk is curvilinear,
increasing geometrically with increasing consumption.
Alcohol is a potent teratogen. The most serious consequence of drinking during pregnancy is fetal alcohol syndrome, a developmental disorder characterized by craniofacial abnormalities, growth retardation, and nervous system impairments that may include mental disability.
Alcohol affects brain development, a process under tight temporal and spatial constraints, with each brain region having its own timetable for development. Alcohol has been shown to selectively exert its effects at the cellular and molecular levels on these developmental processes. Adolescents and young people are particularly vulnerable to the harmful effects of alcohol (11). During adolescence, alcohol can lead to structural changes in the hippocampus (a part of the brain involved in the learning process). Repeated alcohol use can expose the liver to hypoxia, harmful products of alcohol metabolism and reactive oxygen chemicals, and protein adducts.
In addition, alcohol increases the levels of circulating lipopolysaccharides,
which, together with the above toxins, cause liver damage. Alcohol can also exacerbate hepatitis C. More than half of all patients with hepatitis C have a past history of alcohol use, and chronic alcohol consumption of more than five drinks per day in individuals with hepatitis C increases the rate of liver fibrosis, and the risk for cirrhosis, hepatocellular carcinoma and, possibly, death from liver disease (12).
Alcohol has been identified by the International Agency for Research on
Cancer (IARC) as carcinogenic to humans (13). Several mechanisms have been identified for alcohol-associated carcinogenesis, including acetaldehyde formation, induction of CYP2E1 leading to formation of reactive oxygen species and enhanced pro-carcinogen activation, and modulation of cellular regeneration. Because of repeated exposure to acetaldehyde after alcohol
consumption, individuals with inactive ALDH2 are at increased risk for
upper gastrointestinal cancers. Chronic alcohol use can lead to adverse immunological consequences.
Numerous studies have documented wide-ranging deleterious effects on both innate and adaptive immunity from acute and chronic alcohol use. People with alcohol dependence are often immunodeficient and have an increased incidence of infectious diseases. Bacterial pneumonia, for example, is a leading cause of lower respiratory tract infection in this population.
With respect to heart disease, it seems that the effects of alcohol are both positive and negative. Epidemiological studies have found a preventive effect of regular light drinking (as little as a drink every second day), although the finding remains controversial (14, 15), and appears to be confined to males over the age of 45 years and females past menopause. However, heavy drinking bouts are associated with increased rates of heart attacks. Even in societies where heart disease is a very important cause of death, the overall number of lost years of life attributable to drinking outweighs the saved years attributable to protective effects.