Most GI adversities associated with drinking beverages containing alcohol come with excess, and virtually all are caused by alcohol in particular. In some cases, the effect of wine is different from that of other drinks–watch for them. The ineffable morning-after distress following indiscretion is poorly understood and is transient, but unpleasant consequences of heavy drinking may be lasting and as severe as cancer.

The all-too-common chief complaint of the oesophagus (gullet) is heartburn, caused by welling up of acid material from the stomach. Two major determinants of such acid reflux are the quantity of acid secreted by the stomach and the propulsion of the stomach acid the wrong way, upward into the oesophagus instead of downward into the intestine. Wine may stimulate heartburn: it stimulates acid production by the stomach. Alcohol does not. Here is a rare example of an unfavourable effect of wine’s special attributes, presumably polyphenolic antioxidants. Alcohol, however, especially in heavy dose, may relax the lower oesophageal valve (sphincter) that is supposed to seal off the oesophagus, and disorder motility, thereby promoting reflux.

Cirrhosis of the liver of any cause, including abuse of alcohol, is often complicated by formation of oesophageal varices, dilation of veins of the lower oesophagus, a distinct risk of life-threatening haemorrhage. The stomach is both a key actor and a target in the life of ingested alcohol. Alcohol dehydrogenase, the enzyme that first metabolizes alcohol, so neutralizing it, is secreted by the gastric mucosa, the lining of the stomach. When ample alcohol slows the emptying of the stomach, alcohol dehydrogenase has more time to attack the alcohol.

Women’s stomachs contain about 60 percent as much alcohol dehydrogenase as do men’s, likely the chief reason for the long-observed lesser tolerance of women for alcohol and the recommendation that their safe and healthy portion should be about half of men’s. So, when a couple share a bottle of wine at dinner, he should get two-thirds.

Binge drinking of high-proof beverages may lead to acute gastritis, inflammation of the stomach, sometimes accompanied by haemorrhage. Wine and beer are innocent, and may be protective.

The intestines, large and small, are not just inert pipes conveying food and the products of digestion to their fate. Their linings actively secrete digestive enzymes and absorb the nutrients made available by digestion. Their muscular walls churn and propel the contents to enhance the chemical reactions of digestion. The muscular motility of the intestine may be reduced in alcoholics, thereby unpredictably altering function and allowing toxic bacterial overgrowth. An odd converse has been observed recently in overweight mice, whose obesity slows intestinal motion. The bacteria that grow to excess as a result produce alcohol, and these mice develop liver abnormalities similar to those of obese humans and to alcoholics. The lesson may be that obesity and alcohol are collaborators in causing liver disease–take heed.

Surprisingly, light-drinking laboratory rats have exhibited enhanced liver regeneration after injury compared to rats who abstained or who drank more. Heavy doses of alcohol may impair intestinal absorption of nutrients, including thiamin, vitamin B12 , amino acids (the building blocks of proteins), perhaps calcium and zinc, leading to complex malnutrition..

Iron absorption may increase with drinking, not necessarily harmless, for excessive iron may injure the liver. Excessive drinking often leads to diarrhoea.

That wine, especially, and other alcohol-containing beverages help prevent gastro-intestinal infections has been known for a very long time. Claret, drunk in British army messes in India, was held to be "a sovereign preventative against the prevalent cholera", just one of a number of similar observations here and there over the years. More recently and more scientifically, wine has been demonstrated to be an effective inhibitor of a trio of fearsome bacteria, Escherichia coli, Salmonella, and Shigella, causes of "traveller’s diarrhoea" and worse, typhoid and related diseases, and bacillary dysentery, respectively. Researchers suspect that the operative benefactor is one, or more, of wine’s polyphenols. Wine and spirits, but not beer, consumed with raw oysters contaminated with hepatitis A virus, which enters via the gastro-intestinal tract, were associated with a reduced risk of infection.The bacterium Helicobacter pylori (H.pylori) looms, much to the astonishment of the medical profession, a malign superstar of the first magnitude. It resides in the stomachs of those infected. Who could have imagined that this organism causes much of chronic gastritis, a large majority of peptic ulcers, and a substantial proportion of cancers of the stomach? H. pylori is now being implicated as a promoter of our most deadly disease, atherosclerosis, cause of heart attacks, strokes, and other catastrophes. Drinking, especially of wine, appears to help eliminate H. pylori. In a direct study, less than one-third as many drinkers as abstainers were infected.

H. pylori infection is also associated with reduced activity of alcohol dehydrogenase in the stomach. After eradication of the infection, alcohol dehydrogenase normalizes within two months. Alcohol is the only component of wine that has been clearly shown to increase the risk of some cancers, and then only when abused.

Chronic heavy drinking, particularly accompanied by abuse of tobacco, is associated, in the gastro-intestinal tract, with increased cancer risk in the mouth, throat, oesophagus, and perhaps the upper stomach. Inconclusive reports have raised the question of a slight increase in risk of cancer of the pancreas. The data relating beer and spirits to a possible slight increase of risk of colorectal tumours are conflicting and confusing.

Might moderate drinking protect against cancer? Early indications suggest the answer might be "yes". A number of studies has demonstrated that wine, in particular, possesses several properties that would tend to prevent or inhibit cancer, no doubt through the actions of its antioxidant compounds. Epidemiologic research has revealed substantial reduction of risk of cancers of the oesophagus and upper stomach and colon and rectum in wine drinkers as compared to non-drinkers.

In essence, past experience and current research indicate that abuse of alcohol risks damaging the gastro-intestinal tract at several points, but moderate wine consumption risks only a little heartburn, while possibly leading to major health benefits, not to mention gustatory pleasures.

Whether wine is a poison, a medicine or a nourishment is a matter of dosage. –Paracelsus

Harvey E Finkel M.D is Clinical Professor of Medicine at Boston University Medical Centre and is a member of AIM’s Social, Scientific and Medical Council