Alcohol and cancer: the evidence

The International Agency for Research into Cancer (IARC; part of the World Health Organisation) has classified alcohol as a Group 1 carcinogen since 1988. 1 IARC's rulings are the gold standard in terms of determining if something causes cancer, and Group 1 is their highest risk category. It means that there is convincing evidence that alcohol causes cancer in humans. More recent reviews by IARC and other agencies have also concluded that drinking alcohol causes cancer. 2, 3, 4, 5, 6

A study published in 2011 found that alcohol is responsible for around 4% of UK cancers, about 12,500 cases per year. 7

Alcohol increases the risk of cancers of the mouth, pharynx (upper throat), larynx (voice box) and oesophagus (foodpipe). 8

One review found that people having 4 or more drinks (where one drink has around 1.5 units of alcohol) a day had about 5 times the risk of mouth and pharynx cancers compared to people who never drank or drank only occasionally. And the same review also found that even lighter drinkers of no more than 1 drink a day had a 20% higher risk.9

Even small amounts of alcohol can increase the risk of breast cancer. A review of the evidence in 2012 concluded that having 1 drink a day (around 1.5 units) could increase the risk of breast cancer by 5%. 10 And the risk increases the more a woman drinks, several studies have found that each additional 10g of alcohol drunk a day increases the risk by about 7 - 10%. 11, 12, 13

Alcohol is one of the main risk factors for liver cancer. 14 Heavy drinking can lead to cirrhosis, a condition where the liver is repeatedly damaged and scar tissue builds up. Cirrhosis increases the risk of liver cancer.

And alcohol aggravates the risk of liver cancer in people with hepatitis B or C infections who are already at higher risk. People with these infections should avoid alcohol, as even small amounts could damage their livers. 15

Studies have shown that alcohol can increase the risk of bowel cancer. 8, 16 Even fairly small amounts can have an effect, the EPIC study found that for every 2 units a person drinks each day (less than a pint of premium lager or large glass of wine) their risk of bowel cancer goes up by 9%. 17

At the moment, we are not entirely sure how alcohol acts to cause different types of cancer but there are several theories with good evidence. It is likely that alcohol causes different types of cancer in different ways. 18

The theory with the strongest evidence is related to how our bodies process alcohol. It is converted into another chemical called acetaldehyde, which is the substance behind hangovers. And acetaldehyde can also cause cancer by damaging our DNA and preventing it from being repaired. 19 The International Agency for Research into Cancer (IARC) classes acetaldehyde associated with drinking alcohol as a Group 1 substance, which means it can cause cancer in humans. 6 Drinking alcohol greatly increases the level of acetaldehyde found in saliva. 20 And a small initial study in 2012 found higher levels of DNA damage in the mouth cells of people after drinking alcohol. 21

Alcohol can increase the level of hormones such as oestrogen in the body. 22, 23, 24 Unusually high levels of oestrogen could cause breast cancer. 25

Alcohol can cause cirrhosis of the liver, by repeatedly damaging the liver's cells. This is turn can cause liver cancer. 14

Alcohol makes it easier for cancer-causing chemicals, such as those found in tobacco, to be absorbed in the mouth or throat. 26

Alcohol reduces the amount of folate in our blood. Folate is a B vitamin that our cells need to create new DNA correctly. 27

Alcohol can cause highly reactive molecules known as Reactive Oxygen Species or ROS, to be produced in our bodies and particularly in the liver. 14, 19 These molecules are damaging and they are usually kept at a low level, but when ROS levels are raised, they are known to damage DNA.

Tobacco is another cause of mouth, foodpipe and liver cancers and scientists have found that the effects of alcohol and tobacco together are much worse than either by itself. 3, 28

A meta-analysis published in 2012, which combined the results of 49 previous studies, found that non-smokers who drank alcohol were around a third more likely to develop mouth and upper throat cancer than those who didn't drink alcohol. But smokers who also drank were nearly 3 times as likely to develop the disease. 29 Another study found that the risk of liver cancer was almost 10 times greater in people who smoked and drank heavily. 30

Research has shown that all types of alcoholic drinks, including wine, beer and spirits, can increase the risk of cancer. 2, 6, 31 The risk is linked to the actual alcohol (ethanol) in the drink, and increases with the amount drunk. 8

The more alcohol someone drinks, the more their cancer risk increases. 8 But even quite small amounts of alcohol, around 1 drink a day, can increase cancer risk. 9, 10, 32, 33 Expert reports have concluded that there is no lower limit of alcohol drinking where cancer risk isn't increased. 3, 4

Drinking small amounts of alcohol can offer some protection for people who are at risk of heart disease, which normally applies to people over the age of 40. 34 A review published in 2011 of 84 studies found that although drinking up to 15g of alcohol a day (about 2 units) reduced the risk of dying from heart disease and stroke, the benefits quickly start to disappear as drinking levels increase. 35 A study has calculated that the best balance between benefits and harms is for people who drink less than 1 unit a day. 36

Because of this many sources, including the European Code Against Cancer and the World Cancer Research Fund, have suggested that women should drink no more than one drink a day, and men should drink no more than 2 drinks. 3, 37 Similarly, the UK government recommends that men don't regularly drink more than 3 - 4 units in a day, and women no more than 2 - 3 units. 38 While these levels can increase the risk of cancer, the effects are likely to be small.

Most research into the links between alcohol and cancer has looked at the total amount people drink. This research has found that the more a person drinks, the more their cancer risk increases. Much less research has been done into the effect of pattern of drinking, for example whether drinking is spread evenly across the week or concentrated in binges. At the moment, this research does not point in any clear direction. As the number of studies grows, we should be able to better decide whether the pattern of drinking has any effect on cancer risk or health generally. 5, 39, 40

The risk of alcohol-related cancers increases the more you drink. So by cutting down on what you drink, you could reduce the risk of these cancers.

If you are a heavy drinker, it is not too late to start cutting down. Scientists have found that the risk of mouth, throat and oesophageal (foodpipe) cancers reduces over time in people who have given up drinking. 41, 42

Some studies have found that the children of women who drank alcohol during pregnancy had an increased risk of one type of leukaemia. 43 It is not yet possible to say for sure whether there is a real link, more studies involving larger numbers of people are needed to investigate.

Drinking alcohol during pregnancy has been linked to many other conditions and NICE currently recommend that women stop drinking alcohol altogether while trying to conceive and for at least the first 3 months of their pregnancy. After that time, pregnant women should have no more than a small drink once or twice a week and should avoid binge drinking or becoming drunk. 44