Do antibiotics cause cancer?

New research from America suggesting a link between antibiotics and breast cancer is a timely reminder that antibiotic-resistant superbugs aren't the only worrying legacy of decades of careless prescribing.

Researchers at the University of Washington looked back through the medical notes of more than 10,000 women and found that antibiotic usage was higher in those who had developed breast cancer.

The increased risk was small, and the importance of the link has been played down by UK breast-cancer experts, but the findings add weight to recent studies that have found links between antibiotics and other diseases. In the past year, heavy antibiotic use has been linked to the inflammatory bowel disorder, Crohn's disease, and to children developing allergies such as hayfever and asthma.

As yet, there is no clear consensus as to how antibiotics might encourage the development of these diseases, but one theory is that it is down to their effect on the bacteria that colonise our bowels. In the case of breast cancer it's been suggested that the millions of "healthy" bacteria that line our guts help us break down and absorb phytochemicals in fruit and vegetables that protect against cancer. Antibiotics decimate the numbers of these "healthy" bacteria, thereby reducing absorption of these protective nutrients.

These same bacteria play an important role in the immune system and this may explain the link with inflammatory bowel disease and the development of allergies - children prescribed a broad spectrum of antibiotics early in life were found to be up to 11 times more likely to develop asthma than those who weren't.

Whatever the reason behind such links - and there could be many other factors at play - studies like these can only add weight to calls for more prudent use of antibiotics.

Thankfully, doctors have already taken heed and the number of antibiotic prescriptions in the UK has fallen by a third in five years, but there is still room for improvement.

In 1996 there were 63 antibiotic prescriptions for every 100 males, and 86 for every 100 females, meaning the average man could expect around 50 courses of antibiotics during his lifetime, and the average woman closer to 70.

The research should also encourage growing interest in the role of the bacteria that live in our bowels and the benefits of dietary measures ( probiotics) to support them. I now routinely advise my patients, particularly younger ones, to take steps to restore their bowel fauna to normal by taking some form of probiotic - typically one of the lactobacilli containing drinks - on completion of a course of antibiotics.