KEY POINTS:
Women who have more than three drinks a day of wine, beer or spirits increase their risk of breast cancer by 30 per cent.
It is not the type of alcohol that counts but the amount, US researchers will tell the European Cancer Conference in Barcelona.
The increased risk associated with a daily consumption of three or more drinks is similar to that from smoking a pack of cigarettes or taking HRT, they said.
Previous studies have provided conflicting results about whether wine drinkers are more prone to breast cancer than spirit drinkers, or vice-versa.
The researchers from Kaiser Permanente, a leading US health maintenance organisation, based in California, suggest they have now settled the matter with one of the largest individual studies on the effect of alcohol on the risk.
The results show that one or two alcoholic drinks a day increases the risk of breast cancer by 10 per cent compared with light drinkers who drank less than one drink a day.
There was no difference between wine beer and spirits and no difference between red and white wine.
Arthur Klatsky, an author of the report, said: "A 30 per cent increased risk is not trivial. To put it into context, it is not much different from the increased risk associated with women taking oestrogenic hormones (HRT). In previous research, we have found that smoking a pack of cigarettes or more a day is related to a similar increased risk."
He added: "Statistical analyses limited to wine preferrers, beer preferrers or spirits preferrers or non-preferrers each showed that heavier drinking compared to light drinking was related to breast cancer risk in each group. This strongly confirms the relation of ethyl alcohol to increased risk."
The researchers studied the records of 70,000 women who had undergone health examinations between 1978 and 1985 of whom 2,829 had developed breast cancer by 2004.
They compared the amount of alcohol drunk and the frequency of drinking as well as the type of drink - wine, beer or spirits - preferred.
Previous research conducted in the UK has shown alcohol increases the risk of breast cancer by 6 per cent for each drink consumed daily.
However, that study, co-authored by Sir Richard Doll, who discovered the link between lung cancer and smoking, found no evidence that smoking contributed to breast cancer.
Drinking in Britain has been rising for a decade and the proportion of women aged 16-24 consuming more than three drinks a day has doubled to 18 per cent.
In July, results from the European Prospective Investigation into Cancer and Nutrition showed people who drank four drinks a day (equivalent to two pints of beer or two large glasses wine) increased their risk of bowel cancer by 25 per cent.
Dr Klatsky said although only a small proportion of women were heavy drinkers, the 30 per cent increase in their risk might mean there were 5 per cent more cases of breast cancer in the population overall.
The health consequences of drinking were complicated because it also protected against heart attacks but different mechanisms were at work, he said.
"We think the heart protection benefit from alcohol is real, and is probably derived from [its effect on] cholesterol, reduced blood clotting and reduced diabetes. None of these mechanisms are known to have anything to do with breast cancer."
All the studies point to the fact that people who drink something live longer than those who drink nothing - teetotallers. But weighing up the risks can only be done by each person for themselves.
The outcome is likely to depend on how much they enjoy drinking n and whether they fear heart disease or cancer more.
"Our findings provide more evidence for why heavy drinkers should quit or cut down," he said.
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