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Women know too little about alcohol's role in increasing breast cancer risk, a study suggests.

Only one in five women attending a breast cancer clinic knew it was a risk factor.

But alcohol consumption is estimated to be responsible for 5-11% of cases.

Cancer Research UK said cutting down on alcohol was one of the best things women could do to reduce their breast cancer risk.

Two hundred women took part in the study, published in the online journal BMJ Open. They were either being screened for breast cancer, or having symptoms checked.

They completed questionnaires on lifestyle-related risk factors. Just under a third knew being obese increased breast cancer risk, and half knew smoking was another risk factor. But only 16% of women in the screening group, and 23% in the symptoms group, knew that alcohol is a risk factor.

More than half of those who drank alcohol (88 out of 152) thought they knew how to estimate the alcohol content of drinks, but less than three-quarters correctly estimated the alcohol content of a standard glass of wine, and just over half correctly estimated the amount in a pint of beer.

The numbers that matter

Breast cancer is the most common cancer in the UK

There are more than 54,000 new cases diagnosed and 11,000 deaths each year

Eight in 100 women will develop breast cancer during their lifetime

Drinking two units of alcohol a day increases the risk to 11 in 100

Around half a million women are seen at clinics to check out potential breast cancer symptoms in the UK each year.

Prof Julia Sinclair, who led the study, said it was an opportunity to give them information that could help reduce their chances of developing the disease.

"Ninety-four per cent of them don't have breast cancer. If you have a family history, you would be referred for monitoring.

"But if you're overweight or drinking more than you should be, people don't say 'there's something you could do about that'.

"Alcohol increases the risk by three per 100 so its a low absolute risk, but it's something that's modifiable,

"This is about empowering women to have the knowledge, so they can make decisions."

Alcohol-free days

Prof Sinclair said women given the all-clear from the clinics would generally be happy to be given information about alcohol risk, as long as they weren't "blamed" for drinking.

Cancer Research UK advises that breast cancer risk increases with each extra unit of alcohol per day.

"It's worrying that most women in this study didn't know alcohol raises the risk of breast cancer, as cutting down on alcohol is one of the best ways people can reduce their risk" said Emma Shields, its health information manager.

"You don't have to give alcohol up completely. Having smaller servings and more alcohol-free days can make a big difference."

She added: "Using breast screening appointments as a time to talk to women about their drinking and cancer risk is an interesting idea, but more research is needed to see how people would react to this, and whether it would actually help reduce cancer risk."

"We need to find ways to support people to drink less without making anyone feel blamed or judged," says Eluned Hughes, a public health specialist at Breast Cancer Care and Breast Cancer Now.

"Breast cancer risk is affected by a combination of our genes, lifestyle choices and events throughout life, and there is never one single cause of the disease.

"But, with many contributing factors, it's vital we support more women to do what they can to help shift the odds in their favour."

How many units of alcohol are in drinks?