January 13, 2014
A study published in the Journal of the American Medical Association in 20o4 looked at the association between the amount of antibiotics used over a 17 year period in 2,266 women and their risk of breast cancer. The association was measured by how many days one had been on antibiotics during the 17 years. The categories (in days) were 0, 1-50, 51-100, 101-500, 501-1000, and > or =1001 days. With the exception of the first category of 0 antibiotics, all categories had an increased risk of breast cancer with the 500 days or more category being linked to a more than double risk of developing breast cancer. In other words, if women had been on 500 days of antibiotics in 17 years they showed a double risk of developing breast cancer. That would be the equivalent of just under 3 (10 day) antibiotics per year. Even those who had taken the equivalent of a one 10-day course every 2 years had a 43% increased risk of developing breast cancer. The authors conclude, " Use of antibiotics is associated with increased risk of incident and fatal breast cancer. It cannot be determined from this study whether antibiotic use is causally related to breast cancer, or whether indication for use, overall weakened immune function, or other factors are pertinent underlying exposures. Although further studies are needed, these findings reinforce the need for prudent long-term use of antibiotics."
Antibiotic use in relation to the risk of breast cancer.JAMA. 2004 Feb 18;291(7):827-35