Tuesday, 17 February, 2004, 15:22 GMT
Antibiotics link to breast cancer [BBC NEWS]
There is concern about over-use of antibiotics
Women who use a lot of antibiotics may be at increased risk of breast cancer, research suggests.
Scientists followed the progress of more than 10,000 women for an average of 17 years.
Those who took antibiotics for more than 500 days during the study, had twice the risk of those who took none.
The research, led by researchers at Group Health Cooperative in Seattle, is published in the Journal of the American Medical Association.
Women should not be deterred from taking antibiotics if their GP thinks it is necessary.
Dr Michelle Barclay
The risk was smaller for women who took fewer antibiotics.
But even women who had between one and 25 prescriptions over an average period of 17 years had an increased risk.
They were about one and a half times more likely to get breast cancer than those who took no antibiotics.
Lead researcher Dr Christine Velicer said more work was required to evaluate whether the increased risk is down to the antibiotics themselves.
She said: "It may be that women who take a lot of antibiotics have some other processes happening in their bodies - such as a weak immune response or a hormonal imbalance -which may be an underlying cause of breast cancer."
Dr Velicer said women who never took antibiotics may be generally healthy, and so less likely to develop cancer, as well as other diseases.
"This possibly could account for some - but probably not all - of the increased breast cancer risk we saw among antibiotic users."
Dr John Potter, of the Fred Hutchinson Cancer Research Center, also worked on the study.
He said it was far too soon to blame antibiotics for an increased risk of cancer - and stressed that they still had an important role to play in the treatment of infection.
However, he also emphasised the fact that the study had uncovered an association between breast cancer and a broad range of antibiotics.
There are various theories about how antibiotics may increase the risk of breast cancer.
One is that antibiotics affect the bacteria in the intestine, interfering with the metabolism of certain foods that are known protect the body against cancer.
Others centre on antibiotics' impact on the body's immune and inflammatory responses.
Dr Michelle Barclay, of the charity Breakthrough Breast Cancer, said: "Breast cancer is an enormously complex disease and we don't yet know all the causes.
"There may be many factors that increase a woman's breast cancer risk and this study provides food for thought.
"However, caution should be exercised when interpreting results, as the reason for taking antibiotics may be the actual risk factor, rather than the drug itself.
"Women should not be deterred from taking antibiotics if their GP thinks it is necessary."
Breast cancer is the most common cancer in women worldwide.