Is there such a thing as a safe dosage of alcohol?

Risks associated with high consumption are clear, but research shows mild drinking can have benefits

The Public Health (Alcohol) Bill, to be enacted by the end of 2015, will include many measures aimed at tackling overconsumption of alcohol in Ireland. While very moderate drinking poses little threat to health (indeed there is evidence it may be good for you), consumption of alcohol beyond a low level is unhealthy.

Chemically, alcohol is ethanol (C2H6O). Tiny amounts of ethanol are naturally present in the human body: about 3g of alcohol per day are produced by fermentation in the gut. The natural concentration of ethanol in blood is 0.1mg-0.3mg per 100ml. The blood-alcohol limit for legal driving is 50mg per 100ml. The detoxification enzymes present in the body break ethanol down to harmless carbon dioxide and water; 90 per cent of detoxification takes place in the liver.

Medicine uses the “unit of alcohol” concept when advising on the health implications of drinking. One unit contains 10g of ethanol, which is equivalent to a half pint of 4.3 per cent alcohol-by- volume beer, a small glass (125ml) of wine or a pub measure (35.5ml) of spirits. Official low-risk alcohol consumption guidelines for adults recommend a limit of 17 units per week for men and 11 units for women. Drinking more than this is termed “hazardous drinking”, and “binge-drinking” (six or more units in a single session) is particularly hazardous.

Overconsumption of alcohol is closely related to 60 different medical diagnoses, including cancer, stroke, heart disease, cirrhosis of the liver and pancreatitis. Drinking two large glasses of wine (250ml) or two pints of strong lager (5.3 per cent alcohol) per day increases the risk of contracting mouth cancer threefold, and women who regularly drink slightly above the recommended guidelines increase their chances of contracting breast cancer by 20 per cent (UK National Health Service).

Dependent on alcohol

Only half the world’s population drinks alcohol. Europe has the highest level of alcohol consumption and alcohol-related harm. Eighty per cent of Irish adults drink, and more than half drink to a harmful extent. Almost 10 per cent of drinkers are dependent; the figure is 15 per cent among 18-24-year-olds. A recent UCC study (

Open, January) showed that two-thirds of students, both male and female, indulge in hazardous drinking, while 17 per cent of males and 5 per cent of females binge-drink at least four times a week.

But there is significant evidence that mild drinking brings cardio-protective benefits to middle-aged and older people. The most recent study, by Alexandra Goncalves and others, followed nearly 15,000 people, average age 54 years, over a 15-year period (published online in European Heart Journal). None of the participants showed symptoms of heart failure prior to the study. It shows 61 per cent of participants were former drinkers or teetotalers, 25 per cent drank up to 10 units of alcohol per week, 8 per cent drank 10-20 units, 3 per cent drank 20-30 units and 3 per cent drank more than 30 units per week. Compared to alcohol abstainers, the study showed that men who drank up to 10 units per week had a 20 per cent reduced risk of heart failure and women who drank up to seven units had a 5 per cent reduced risk of heart failure. In the higher drinking categories, the risk of heart failure was not significantly different from abstainers.

A close relationship has been established between alcohol and cancers of the mouth, pharynx, larynx, oesophagus, colon, rectum, liver and breast. The World Health Organisation says that, when it comes to cancer, no amount of alcohol is safe.

My UCC colleague Jim Heffron, emeritus professor of biochemistry and the author of numerous peer-reviewed publications in toxicology, says: “There is strong evidence for a causal relationship between alcohol consumption and several cancers, but there is some uncertainty of the molecular mechanism; hence whether there is a safe dose of alcohol or not is open to question. It is also important to note that there is a synergistic effect between alcohol and smoking with respect to the risk of certain cancers.”

Alcohol largely obeys the “dose makes the poison” principle introduced by Paracelsus (1493-1541), the Father of Toxicology, who wrote: “All substances are poisonous; there is none which is not a poison. The right dose differentiates a poison from a remedy.”

William Reville is an emeritus professor of biochemistry at UCC, understandingscience.ucc.ie