The risk of developing prostate, breast, lung, and colon cancer rises with use of antibiotics, a large observational study, published in the International Journal of Cancer, has found.
And the risk of less common cancers has also been found to be linked to antibiotic use - non-melanoma skin cancer, duodenum, pancreas, kidney, bladder and male genital cancers other than prostate. Thyroid cancers, myeloma and leukaemia were more than 1.5 times as likely among study participants who had received six or more antibiotic prescriptions, compared with those who had less exposure. The study is based on more than three million people and more than 100 000 cases.
The Finnish nationwide cohort study included 3 112 624 men and women aged 30-79 years with no history of cancer, whose use of antibiotics was obtained from the drug prescription registry. During seven years of follow-up, from 1998 to the end of 2004, a total of 134 070 cancers were identified.
Compared with 0-1 prescriptions, for 2-5 and six prescriptions of antibiotics the relative risks of cancer were 1.27 (95% confidence interval 1.26 to 1.29) and 1.37 (1.34-1.40). The association was found in men (relative risk between lowest and highest exposure group 1.47, 1.42 to 1.53) and women (1.31, 1.28 to 1.35).
Possible reasons for this finding are that antibiotics themselves may be carcinogenic. The authors say that although evidence is limited, studies in animals have shown that exposure to antibiotics may promote the development of tumours in liver and breast.
Another possibility is that antibiotic treatment may disturb protective intestinal microbiota. They may increase the bacterial production of toxins and reduce the number of bacteria that prevent the development of tumours. They may also interfere with oestrogen metabolism, which could affect the risk of hormone dependent cancers. Another theory is that antibiotic treatment, especially if long term, may have a detrimental effect on immune defences, which could compromise defences against cancer.
