A glass of wine a day doubles a woman's risk of developing a common type of breast cancer, say scientists.
Women drinking just seven units of alcohol a week - half the recommended safe level - have a much increased chance of developing lobular cancer, compared to those who don't drink at all, reports
Lobular cancer is the second most common form of breast cancer and is the most common in women between 45 and 55 years. It affects the lobes deep inside the breast tissue and can be hard to detect, so is often quite advanced by the time it is diagnosed.
Around 40,000 women a year in Britain are diagnosed with breast cancer. The disease affects one in nine women at some point in their lives.
Cancer epidemiologist Christopher Li said: "We found women who drank one or more drinks per day had about double the risk of lobular type breast cancer but no increase in their risk of ductal type breast cancer."
Young women have a low risk of developing breast cancer and so even if they drink a reasonable amount of alcohol the risk still remains relatively low. But for older women the effect of alcohol is more significant.
The researchers looked at the tumour types of 2,944 breast cancer patients and their alcohol consumption. Drinkers were grouped into six categories according to the average number of drinks per week starting from less than one to more than fourteen.
Scientists found that alcohol was more strongly related to the risk of lobular cancer than cancer in the milk ducts.
The risks observed did not vary by the type of alcohol women consumed.
Researchers at the Fred Hutchinson Cancer Research Centre in Seattle said: "It is important to note that ductal cancer is much more common than lobular cancer accounting for about 70 percent of all breast cancers whereas lobular cancer accounts for only about 10-15 percent of cases."