ROCHESTER, Minn. An observational study has linked the use of antibiotics before the age of 2 with an elevated risk of a developing wide range of health conditions later on during childhood.

The retrospective case study was conducted reviewing the 14,500 records within the Rochester Epidemiology Project, 70% of whom had received the medications, and published Monday, Nov. 16, in the journal Mayo Clinic Proceedings. It followed children for 8 years, some as long as 14 years.

The study, which only can show association and is not proof of causality, found that children given antibiotics before age 2 were more likely to develop one or more conditions including asthma, seasonal and food allergies, celiac disease, atopic dermatitis, ADHD and obesity.

The diversity of the illnesses is notable. As a broad mix of immune, metabolic and behavioral conditions, the ailments do not outwardly appear to share a common bodily mechanism that would be affected by antibiotics, which kill bacteria and therefore alter the body's natural collection of bacteria.

The authors believe the study sheds light on the wide-ranging effects of disrupting the microbiome, a complex collection of good bacteria which have been shown to regulate a host of bodily mechanisms. Rodent studies, for instance, show that early use of antibiotics affects bodily composition.

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"Clearly in the first two years of life we have profound development going on of our immune system, cognition, behavior and neurodevelopment," said Nathan LeBrasseur, a researcher on aging at Mayo Clinic and lead author on the paper.

"These bugs have been linked to a host of outcomes, from tooth and gum disease, to allergies and other conditions in adults. We think when we manipulate these bacteria in children there's this incredible vulnerability for development. We're shifting that homeostasis, a disruption in balance that can have profound effects."

"Those bugs have so much information in them, and communicate with our developing bodies," LeBrasseur said. "That can influence the development of these different diseases."

Though the study cannot prove that antibiotics lead to the conditions, the association was strengthened by the study having excluded children with illness before receiving antibiotics.

The study also controlled for a host of potential confounding contributors to risk, such as sex of the child, ethnicity, birth weight, mother's age, smoking status, education levels and use of antibiotics during pregnancy.

"We saw a dose response," LeBrasseur adds. "Kids that were getting multiple prescriptions during childhood were at even greater risk for these conditions." The authors also noted an effect of specific antibiotics on specific conditions.

It did not take into account breastfeeding, diet, physical activity, sleep, other medications or familial factors.

Many antibiotics are given to children for respiratory infections that are likely viral in nature — i.e. common colds — and therefore inappropriate.

Reviews of patient records show that 25% of antibiotic prescriptions for young children are inappropriate, and 35% are potentially used in error as they fit no diagnostic code.

LeBrasseur believes both clinicians and parents should think twice before prescribing or asking for antibiotics for young children.

"I do think there needs to be better education to providers about the potential health risks of antibiotics," he said. "There's an awareness now of multi-drug resistance in older adults ... but there is much less attention to the potential for risk in children. There's this widely held belief that there's no risk," he adds. "We know for a fact that's not true."

"We can't say drug A caused disease B, but it generates a number of questions about what are the drugs doing that influence health," he said. "We're hopeful it will guide clinical decision making."