Risk of breast cancer? Yoghurt, milk could come to your rescue

Including probiotic-rich dairy products such as yoghurt and milk in diet may help protect women against breast cancer, a new study suggests.

Bacteria that have the potential to abet breast cancer are present in the breasts of cancer patients, while beneficial bacteria are more abundant in healthy breasts, where they may actually be protecting women from cancer, researchers said.

These findings may lead ultimately to the use of probiotics such as yoghurt and milk to protect women against breast cancer, they said.

Scientists from Lawson Health Research Institute in Canada obtained breast tissues from 58 women who were undergoing lumpectomies or mastectomies for either benign (13 women) or cancerous (45 women) tumours, as well as from 23 healthy women who had undergone breast reductions or enhancements. They used DNA sequencing to identify bacteria from the tissues and culturing to confirm that the organisms were alive.

Women with breast cancer had elevated levels of Escherichia coli and Staphylococcus epidermidis, are known to induce double-stranded breaks in DNA in HeLa cells, which are cultured human cells, researchers said. "Double-strand breaks are the most detrimental type of DNA damage and are caused by genotoxins, reactive oxygen species, and ionising radiation," said researchers.

The repair mechanism for double-stranded breaks is highly error prone, and such errors can lead to cancer's development. Conversely, Lactobacillus and Streptococcus, considered to be health-promoting bacteria, were more prevalent in healthy breasts than in cancerous ones. Both groups have anticarcinogenic properties, researchers said.

For example, natural killer cells are critical to controlling growth of tumours, and a low level of these immune cells is associated with increased incidence of breast cancer. Streptococcus thermophilus produces anti-oxidants that neutralise reactive oxygen species, which can cause DNA damage, and thus, cancer, researchers said.

The motivation for the research was the knowledge that breast cancer decreases with breast feeding, said Gregor Reid from Lawson Institute. Lactation might not even be necessary to improve the bacterial flora of breasts.

"Colleagues in Spain have shown that probiotic lactobacilli ingested by women can reach the mammary gland," said Reid.

"Combined with our work, this raises the question, should women, especially those at risk for breast cancer, take probiotic lactobacilli to increase the proportion of beneficial bacteria in the breast?," he said.

Besides fighting cancer directly, it might be possible to increase the abundance of beneficial bacteria at the expense of harmful ones, through probiotics, he added. The findings were published in the journal Applied and Environmental Microbiology.