SEATTLE, WASHINGTON. Antibiotics are effective in treating bacterial infections, but have no effects on viral and other non-bacterial infections. Yet, in 1995 over 22 million prescriptions for antibiotics were issued for non-bacterial, acute respiratory infections in the United States alone. It is clear that antibiotics are being vastly over prescribed and this makes the possibility of an association between breast cancer and antibiotics use of even greater concern.
Researchers from the University of Washington and the Fred Hutchinson Cancer Research Center recently reported a clear association between the risk of breast cancer and exposure to antibiotics. Their study involved 2266 women with primary, invasive breast cancer and 7953 randomly selected age-matched controls. The researchers found that women who had been exposed to antibiotics for 1-50 days had a 45% greater relative risk of developing breast cancer and dying from breast cancer than did women who had never used antibiotics. Women who had used antibiotics for more than 1,000 days in their lifetime had double the risk.
The researchers point out that it is not clear whether the observed association is due to the fact that
antibiotics actually promote breast cancer or whether the increased risk stems from the underlying condition
(infection, inflammation) that is being treated with the antibiotic. Antibiotics are known to disturb the
intestinal microflora and interfere with the metabolism of phytochemicals that may help prevent cancer. The
antibiotic tetracycline may be associated with an increased production of inflammatory prostaglandins. The
researchers found no difference in association between breast cancer and antibiotic-use among
premenopausal versus postmenopausal women and the type of antibiotic used did not alter the strength of
the association either. They conclude that their findings lend further support to oft-repeated warnings to limit
the prescription of antibiotics as much as possible and not prescribe them for non-bacterial
Editor's comment: It seems to me that the observed association could well involve candida overgrowth. Frequent and prolonged use of antibiotics will almost certainly lead to an overgrowth of candida (yeast infection). Candida, like alcohol, is a potent generator of aldehyde and both alcohol itself and its metabolite, acetaldehyde, have been linked to an increased risk of breast cancer. I have seen no medical evidence of a possible candida connection, but to be on the safe side it is a good idea to take probiotics (acidophilus) when taking antibiotics unless there is a specific reason not to.