Just half a glass of wine a day may increase breast cancer risk
"Just half a glass of wine a day ups the risk of breast cancer by nine per cent, experts warn," The Sun reports. A major report looking at global evidence found that drinking just 10g of alcohol a day – 1.25 units – was linked to an increased risk of breast cancer.
The report was produced by the World Cancer Research Fund which reviews the global evidence on the link between diet, weight, physical activity and breast cancer. Overall, this report supports what is already known, that alcohol consumption is a risk factor for breast cancer.
The report found that for each 10g of pure alcohol consumed each day, the risk of premenopausal breast cancer increases by 5%, and the risk of postmenopausal breast cancer increases by 9%. Experts have suggested that this would equate to about one extra case of cancer per 100 women, based on current rates of breast cancer in the UK.
After a recent review by expert groups of the evidence on all of the health effects of alcohol, the UK Chief Medical Officer's advice is that men and women should not regularly drink more than 14 units in a week to try and keep overall risks at a low level.
What is the basis for these current reports?
These news stories are based on a report from the not-for-profit World Cancer Research Fund (WCRF). The WCRF has an ongoing project to regularly assess the evidence on links between diet, nutrition, physical activity and different types of cancer, and provide recommendations based on this. Its current report is an update on the links between these factors and breast cancer in women.
To prepare the report, the WCRF systematically searched for relevant studies published since its last update in 2010. It looked at randomised controlled trials, cohort studies and nested case control studies.
These new studies were assessed by a panel of independent international scientists to see if they should be included in this latest report.
Those that were relevant were then interpreted along with the older evidence in the previous WCRF reports. They carried out statistical pooling of the study results where possible. All together the panel considered 119 studies looking at more than 12 million women, and over 260,000 cases of breast cancer.
What impact did the report find for alcohol on breast cancer risk?
Premenopausal breast cancer
The report identified eight new or updated studies on the link between alcohol and premenopausal breast cancer. Premenopausal breast cancer cases account for around one in five cases of breast cancer in the UK.
It was possible to pool the results of 10 studies on premenopausal breast cancer, and this showed that an additional 10g of ethanol (pure drinking alcohol) a day increased risk of premenopausal breast cancer by 5% (relative risk [RR] 1.05, 95% confidence interval [CI] 1.02 to 1.08).
Postmenopausal breast cancer
The report identified 21 new or updated studies on the link between alcohol and postmenopausal breast cancer. Of these studies, 22 could be pooled, showing that an additional 10g of ethanol (pure drinking alcohol) a day increased risk of postmenopausal breast cancer by 9% (RR 1.09, 95% CI 1.07 to 1.12).
One unit of alcohol is 8g and is equivalent to about:
- half a small glass (76ml) of standard 13% ABV (alcohol by volume) wine
- 218ml of standard 4.5% cider
- 250ml of standard 4% beer or standard 4% alcopop
- 25ml of standard 40% whiskey
Drinking 10g of ethanol every day for a week would be equivalent to 8.75 units of alcohol, which is less than the UK's current maximum upper limit for women. The UK Chief Medical Officer's advice is that, to keep overall risks from alcohol at a low level, it is safest that men and women do not regularly drink more than 14 units in a week.
The report concluded there is strong evidence that consuming alcoholic drinks probably increases the risk of premenopausal breast cancer, and convincing evidence that it increases the risk of postmenopausal breast cancer.
What does this actually mean in terms of numbers of women with breast cancer in the UK?
The report itself did not estimate how many extra cases of cancer this was equivalent to. One expert from the UK, Professor Kevin McConway, Emeritus Professor of Applied Statistics from The Open University said:
"...according to Cancer Research UK, of 100 UK women, about 12 or 13 will develop a breast cancer at some point in their lives. Imagine that these 100 women all drank an extra small glass of wine or half a pint of beer every day, compared to what they drink now. On WCRF's figures, that would lead to 1 more of them developing a breast cancer during their lifetime."
To put this into context, Professor McConway added: "Any increase is a bad thing, but it's only one more out of the 100 women, and that has to be set against whatever pleasure the women might obtain from their drinking. Drinking alcohol has a greater effect on the risks of several other cancers (such as cancers of the mouth, oesophagus and bowel) than it does on the risk of breast cancer, so there are other reasons to give up or cut down, but that just shows the importance [of] looking at the whole picture and not just at breast cancer."
What about other factors?
The report also reported on other factors that could influence risk of breast cancer.
Exercise
The report found strong evidence that vigorous physical activity (enough to get you out of breath) probably decreased risk of premenopausal breast cancer. There was also strong evidence that physical activity as a whole, including vigorous and less strenuous exercise, probably decreased risk of postmenopausal breast cancer.
Breastfeeding
The report found strong evidence that breastfeeding probably decreased risk of breast cancer overall.
Diet
There was limited evidence that including the following in your diet may reduce your risk of breast cancer:
- non-starchy vegetables
- dairy products (for premenopausal breast cancer only)
- foods containing carotenoids, such as carrots, spinach and kale
- foods high in calcium, such as sardines and broccoli
Body weight
The relationship between body weight and breast cancer risk seemed to be complex.
For premenopausal breast cancer, greater body fatness during adulthood actually had a protective effect. More body fatness between the ages of 18-30, also had a protective effect against postmenopausal breast cancer risk.
However, greater body fatness during adulthood as a whole, and greater weight gain during adulthood increased postmenopausal breast cancer risk.
So, the WCRF continues to maintain its advice that we should keep our weight in the healthy range for as long as possible for overall cancer prevention.
Read more about breast cancer prevention.
