Can soya help reduce risk of breast cancer?

New research by Cancer Research UK appears to confirm a long-suspected benefit of eating soya - it can help reduce the risk of breast cancer.

Soya has received a lot of good press in recent years as a result of research showing its effects on health, including reducing the symptoms of the menopause in women. Previous studies had suggested that the soya-rich diet of women in China and Japan could be responsible for the lower incidence of breast cancer in those countries, but research had always proved inconclusive.

But the latest research, carried out by Cancer Research UK in association with the National University of Singapore and the US National Cancer Institute, appears to confirm that there is a link between soya and lower breast cancer risk and suggests a possible reason for the protective effect.

The researchers combined data from two studies of women living in Singapore in order to analyse in detail the effects of diet on women's breast tissue.

The first study focused on women's eating habits, including their intake of soya, while the second used mammograms to classify women according to the density of their breast tissue. Previous research had shown that dense tissue, which can be observed with a breast X-ray, is associated with an increased risk of breast cancer.

By identifying a group of 406 women who took part in both these studies, the researchers were able to see how diet affected breast tissue and tell who was most likely to develop breast cancer. They found that women who ate the most soya were 60 per cent less likely to have 'high risk' breast tissue than women with the least soya in their diet.

The study's co-author, Dr Stephen Duffy of the Cancer Research UK's Mathematics, Statistics and Epidemiology Department in London, said: "There has always been a question mark over a connection between soya and breast cancer - some studies have suggested a link but others haven't.​

"This research shows for the first time how the amount of soya a woman eats may have an affect on breast tissue and in turn may potentially reduce her risk of breast cancer."​

The reason why the soya is thought to help reduce the risk of breast cancer is related to the isoflavones in soya, chemicals which mimic the action of the female hormone oestrogen. Scientists believe that the isoflavones in soya can help lengthen a woman's menstrual cycle, and previous research has suggested that the fewer menstrual cycles a woman goes through in her lifetime, the lower her risk of breast cancer.

Sir Paul Nurse, interim chief executive for Cancer Research UK​, said: "Breast Cancer now affects nearly 40,000 women in the UK every year making it the most common form of cancer. That's why it's vital that we find new ways of preventing the disease. These findings make an important contribution towards our ongoing studies on the relationship between diet and cancer and may eventually point to new ways of preventing breast cancer."​

The research is published in the latest issue of Cancer Epidemiology, Biomarkers and Prevention​.