For the study, the researchers identified five case-control studies involving 13,069 cases and 73,920 controls from major medical databases like Medline, Cochrane, and EMBASE databases, which they believed were eligible for their meta-analysis.
They found those who ever used antibiotics were 17.5 percent more likely to be diagnosed with breast cancer. A meta-regression analysis also showed a borderline dose-response effect of antibiotics on the risk of breast cancer.
The researchers concluded "this is a finding with potentially important public health implications, which should be further examined in the literature."
One explanation is that women who have ever used antibiotics may have weaker immunity against cancer. It is well known by some researchers that a person's immunity can be a big determinant for his cancer risk.
Early in 2003, Velicer C.M. and colleagues from the University of Washington cited a hypothesis proposed by others in Cancer Causes & Control, which states that antibiotics destroy intestinal microflora that would otherwise metabolise phytochemicals from edible plants into compounds that may protect against cancer.
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