Antibiotics Scare

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s taking antibiotics really double a woman's risk of getting breast cancer? That was the clear impression left by some headlines last week, but that may say more about the dangers of first impressions than it does about antibiotics.

The news sprang from a review of the medical records of more than 10,000 women who belonged to a Seattle-area health plan. The study, published in the Journal of the American Medical Association, compared pharmacy and breast-cancer-screening records and found that women who filled 25 or more prescriptions for antibiotics over a 17year period developed breast cancer at twice the rate of those who took no antibiotics. Moreover, there seemed to be what scientists call a dosage-response trend: among women who took more antibiotics, the death rate from cancer was even higher, as much as 3 1/2 times as great.

But there is a big difference between a statistical link and a causal relationship. It's entirely possible that breast cancer was creating the women's need for antibiotics (rather than the other way around) by undermining the immune system, for example. Or that an underlying problem — perhaps chronic inflammation — was making the women's bodies a breeding ground for both bacterial infections and tumors. It's worth noting that the antibiotics users were, on average, older and heavier, had stronger family histories of cancer and were more likely to use hormone-replacement therapy — all risk factors for breast cancer. It is the sort of study, noted Dr. Roberta Ness in an accompanying editorial, that raises more questions than it answers.

That doesn't mean that there aren't risks in taking antibiotics. The drugs are real lifesavers, but they have been dangerously overused for decades, creating strains of bacteria that are resistant to first-line antibiotics and forcing doctors to use stronger and stronger drugs. Antibiotics should be prescribed only for bacterial infections and not for colds or the flu, which are caused by viruses. Once you start taking an antibiotic, you should always take the full course, even if you start feeling better before finishing the regimen; otherwise you are just adding to the resistance problem. And please don't insist that your doctor give you an antibiotic when it isn't necessary. Many doctors will cave under pressure, but you shouldn't put them in that position. They really do know what is good for you.

Sanjay Gupta is a neurosurgeon and CNN medical correspondent