breast cancerStudies in the US have found that overuse of antibiotics has the potential to alter the normal healthy bacteria living on our bodies and cause an overgrowth of fungi and pathologic or bad bacteria, according to the American Society for Clinical Oncology. 

Diarrhoea, allergic reactions, abnormal heart rhythms, tendon injuries, and yeast infections are some of the consequences from antibiotic use. It now appears that breast cancer also may be related to antibiotic use.

At this year’s annual cancer meeting, researchers compared antibiotic use in 158 women with newly diagnosed invasive breast cancer to a group of 158 women with similar features who were healthy. After controlling for breast cancer risk factors (age, body mass index, smoking, onset of menstruation, number of children, estrogen use, family history, breast feeding etc.), women who used antibiotics for 21 or more days had a 3.5 fold higher risk of developing breast cancer. Use of β lactam antibiotics (e.g. penicillins, cephalosporins, carbapenems, monobactams) was associated with a more than 11 fold higher risk of developing breast cancer and use of macrolides (e.g. erythromycin, azithromycin, clarithromycin) was associated with a nearly three-fold higher risk of developing breast cancer.

Previously, experts postulated that antibiotics affected the bacteria within the intestines which resulted in altered estrogen metabolism and a weakened immune response. Antibiotics also may decrease absorption of cancer protective flavonoids or plant metabolites shown to decrease cancer risk.