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Breast cancer
linked to antibiotic use
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By Peta Rasdien
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A STUDY of
10,000 United States women has shown those who used the most
antibiotics had double the risk of breast cancer.
The fact that the
association was consistent for all forms of antibiotics and the risk went
up with the number of prescriptions was a powerful indication that the link
was real.
Women who had more
than 25 individual prescriptions for antibiotics over an average period of
17 years had twice the risk of breast cancer as those who had taken no
antibiotics.
The risk was lower for
women who took fewer antibiotics, but even those who had between one and 25
prescriptions were about 1.5 times more likely to get breast cancer, the
researchers found.
Experts have been
quick to caution that this should not encourage women to stop taking their
medicines.
There could be other
explanations for the association and much more research was needed before
scientists understood what the surprising results meant, they said.
US National Cancer
Institute senior scientist Stephen Taplin, who
helped conduct the study, said: "This is not saying that women should
stop taking antibiotics. Women should take antibiotics for infections.
"We need to
follow up and find out if this a real association."
Nevertheless, the
study was so well designed and the findings were so striking that it could
be that antibiotic use was an important, previously unrecognised risk
factor for breast cancer.
Experts said
antibiotics could increase the risk of breast cancer by, for example,
affecting bacteria in the digestive system in ways that interfered with the
metabolism of foods that protected against cancer.
Another possibility
was that antibiotics boosted the risk by affecting the immune system or the
body's inflammatory response.
Researchers said even
if it turned out that antibiotics did not increase the risk for breast
cancer, the finding was likely to turn out to be important because it could
lead to the discovery of whatever it was about women who used the drugs
that also appeared to make them prone to the disease.
A small Finnish study
in 2000 which looked at antibiotic use for recurrent urinary tract
infections and breast cancer suggested a similar link.
Cancer Council of
Australia chief executive Professor Alan Coates said even if there truly
was a link between antibiotics and breast cancer the study did not prove a
causative effect.
A low immune system
would make people prone to repeated infections and therefore a lot of
antibiotic use and might also make them prone to getting a cancer,
Professor Coates said.
Women in higher
socio-economic groups who traditionally had more breast cancers might also
be more likely to take antibiotics for frivolous reasons.
"These things are
potential confounders which might be other explanations for what is a real
association but not cause and effect," he said.
"The probability
that the antibiotics are directly causing the cancer is really very low.
"We are a long
way away from being at the point where we would be worried about the proper
use of antibiotics.
"There is a real
possibility of doing harm if we dissuade even one woman from using
antibiotics she needs.
"If she dies of
the infection then we are doing a lot more harm than any risks of breast
cancer."
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-with AGENCIES
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