Thursday, 20 August 2015

More gobbledygook science on alcohol and cancer risk

We would have seen the headlines this week.  Light drinking increases risk of cancer in women. You might have thought you knew that already. So what is it all about?

A large study (that means the cohort was large enough to have some meaning in terms of the population) published in  The BMJ yesterday suggests that even light and moderate drinking (up to one drink a day for women and up to two drinks a day for men) is associated with an increased risk of certain alcohol related cancers in women and male smokers.  It is a study full of nuances and should be taken with a dose of caution.

Overall, light to moderate drinking was associated with minimally increased risk of 'total' cancer in both men and women.

However, among women, light to moderate drinking (up to one drink per day) was associated with an increased risk of alcohol related cancer, mainly breast cancer.  This is not new. We already have sufficient information to conclude that alcohol consumption increases risk of cancers.  The problem is how much alcohol is 'safe' to drink. 

According to Cancer UK,  alcohol causes 7 types of cancer, including breast, mouth and bowel cancers. Essentially, studies have shown that the less you drink the less risk there is of these types of cancer.  When you drink alcohol, cancer-causing chemicals are formed. Alcohol also affects hormone levels and makes cells even more likely to be damaged by for example smoking.  This is what is meant by 'increased risk'.  As Cancer UK stress, not everyone who drinks alcohol will develop cancer. But on   the whole, scientists have found that some cancers are more common in people who drink more alcohol than others. Every year, alcohol causes 4% of cancers in the UK, around 12,800 cases.

Much depends on other risk factors such as smoking. 

The study shows that risk of alcohol related cancers was also higher among light and moderate drinking men (up to two drinks per day), but only in those who had ever smoked. No association was found in men who had never smoked.

Heavy alcohol consumption has been linked to increased risk of several cancers. However, the association between light to moderate drinking and overall cancer risk is less clear. The role of alcohol independent of smoking has also not been settled.

So a team of US researchers based at Harvard T.H. Chan School of Public Health and Brigham and Women’s Hospital in Boston, set out to determine whether light to moderate drinking is associated with an increased risk of cancer.

They used data from two large US studies that tracked the health of 88,084 women and 47,881 men for up to 30 years. They assessed risk of total cancer as well as known alcohol related cancers including cancer of the the colorectum, female breast, liver, oral cavity, pharynx, larynx and esophagus.

Light to moderate drinking was defined as up to one standard drink or 15g alcohol per day for women and up to two standard drinks or 30g alcohol per day for men. One standard drink is roughly equivalent to a small (118ml) glass of wine or a 355ml bottle of beer.

Influential factors, such as age, ethnicity, body mass index, family history of cancer, history of cancer screening, smoking, physical activity and diet were also taken into account.

During the follow-up period, a total of 19,269 and 7,571 cancers were diagnosed in women and men, respectively. The researchers found that overall, light to moderate drinking was associated with a small but non-significant increased risk of total cancer in both men and women, regardless of smoking history.  We should emphasise the conclusion 'small but non-significant'.  This means the study found no effect.

For alcohol-related cancers, risk was increased among light and moderate drinking men who had ever smoked, but not among men who never smoked. However, even in never smoking women, risk of alcohol-related cancers, mainly breast cancer, increased even within the range of up to one drink a day.

This large study sheds further light on the relationship between light to moderate drinking and cancer, says Dr Jürgen Rehm at the Centre for Addiction and Mental Health in Toronto, in an accompanying editorial.  The truth is it doesn't shed much more light at all.  It reaffirms an association between light to moderate drinking of alcohol  with what are already known to be 'alcohol related' cancers in women.  It sheds no further light on why such a link exists.

Indeed, as the authors state 'more research is needed to explore the interaction between smoking and drinking on risk of cancer'.  But 'roughly speaking' women should not exceed one standard drink a day and men should not exceed two standard drinks a day.  So there  you have it!  Note the use of the scientific 'roughly speaking'.  Scientifically 'roughly' means...?

Finally, the author concluded that people with a family history of cancer “should consider reducing their intake to below recommended limits or even abstaining altogether, given the now well established link between moderate drinking and alcohol-related cancers.”   So there you are then, wiser than we were, and you can have a drink to that -  'roughly speaking' of course! 

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