Sept. 30, 2003 - Evidence continues to build for the so-called "hygiene hypothesis" as the latest study shows that babies treated with antibiotics during the first six months of life may be at increased risk for developing allergies and asthma during childhood.
Investigators from Detroit's Henry Ford Hospital report three times as much asthma in high-risk children given antibiotics before the age of 6 months. These children were also almost twice as likely to develop allergies to pets, ragweed, grass, and dust mites by age 7.
Consistent with previous research, living in households with at least two cats and/or dogs during the first year of life appeared to protect the children against allergies and against asthma caused by allergies. But being breastfed for four months or more was found to increase their risk.
Lead researcher Christine Cole Johnson, PhD, presented the findings at the European Respiratory Society's annual conference in Vienna, Austria.
"I'm not suggesting children shouldn't receive antibiotics, but I believe we need to be more prudent in prescribing them for children at such an early age," Johnson noted in a news release. She added that antibiotics are too often prescribed to treat illness for which they have no effect, such as colds and the flu.
Roughly half of the 445 children enrolled in the study had been treated with antibiotics before the age of 6 months. Antibiotic use was recorded from birth, and at age 6 or 7 years the children underwent a battery of tests for allergies and asthma.
Risk was slightly increased for all children treated with antibiotics before 6 months of age, but it was most elevated for those who were found to be at high risk for allergies and for asthma caused by allergies. Clinical epidemiologist and study co-researcher Keoki Williams, MD, MPH, says high-risk children included those who lived in a household with fewer than two cats and/or dogs, had a family history of allergies, or were breastfed for four months or more.
Although breastfeeding has been linked to an increase in allergies and asthma, it's important to note that breastfeeding is associated with a wide array of health benefits and is still the preferred method of feeding young infants.
It is now widely believed that early childhood exposure to bacteria and other infection-causing agents helps protect against allergies and asthma. This hygiene hypothesis suggests that increasingly sterile environments are to blame for the dramatic rise in allergic diseases during the past few decades.
Overuse of antibiotics has been implicated because the drugs kill bacteria in the gut, which may, in turn, weaken the immune system.
"For asthma, especially, exposure to antibiotics that eradicate a wide variety of bacteria seemed to really increase risk," Williams tells WebMD. "[Like antibiotics], breastfeeding is believed to be protective against infections, and if that is so it may be a risk factor for allergies and asthma."
Pediatric pulmonologist Stanley Goldstein, MD, tells WebMD that studies like this one lend credibility to the hygiene hypothesis and give rise to the hope of developing effective interventions to prevent allergies and asthma.
"There are studies going on now looking at whether exposing children to these agents [bacteria and other infections] very early in life is protective against allergic diseases," he says. "Based on the scientific evidence that we have seen in the past few years, there is a lot of optimism that this approach will work."