(CNN) Children younger than two who are given antibiotics are more likely to have a number of ongoing illnesses or conditions later in life, a new study finds.
Babies and toddlers who received one dose of antibiotics were more likely to have asthma, eczema, hay fever, food allergies, celiac disease, problems with weight and obesity and attention deficit hyperactivity disorder later in childhood, according to the study published Monday in Mayo Clinic Proceedings.
Multiple antibiotic treatments below the age of two was associated with a child having multiple conditions, the study found, with the illnesses differing due to the child's gender, age, type of medication, dose and number of doses.
"We want to emphasize that this study shows association, not causation, of these conditions," said senior study author Nathan LeBrasseur, a researcher at Mayo Clinic's Center on Aging. "These findings offer the opportunity to target future research to determine more reliable and safer approaches to timing, dosing and types of antibiotics for children in this age group."
Researchers analyzed data from over 14,500 children who are part of the Rochester Epidemiology Project, a long-term study which analyzes the medical records of volunteers in Minnesota and Wisconsin. Some 70% of the children in the study had received at least one antibiotic, with most receiving multiple antibiotics.
"Among children who received one or two prescriptions, only girls were at significantly higher risk to develop asthma and celiac disease compared to those unexposed," LeBrasseur and his team wrote. "By contrast, receiving three to four prescriptions was associated with a higher incidence of asthma, atopic dermatitis, and overweight in both sexes, ADHD and celiac disease in girls, and obesity in boys."
Babies of both sexes who received five or more prescriptions had "significantly higher risk to develop asthma, allergic rhinitis, overweight, obesity, and ADHD," the study found. Girls were at higher risk of celiac disease.
The study found penicillin, one of the most commonly prescribed antibiotics, was associated with "increased risk for asthma and overweight in both sexes, celiac disease and ADHD in girls, and obesity in boys, whereas they were associated with reduced risk for autism in girls."
Another commonly prescribed antibiotic, cephalosporin, was linked to higher risk for the greatest number of conditions and, "uniquely, autism and food allergies," the study found.
Why would antibiotics have such an impact -- if indeed future studies repeat the connection?
It's possibly due to the disruption of the bacteria in a baby's gut, which is needed for the proper development of the immune system, neural development, body composition and metabolism, LeBrasseur and his team said.
Antibiotics do not discriminate between "good" and "bad" bacteria in the digestive tract, killing all of them and leaving the gut without the appropriate microbiome distribution. We need certain bacteria to absorb nutrients, break down foods in intestines and protect the entire digestive system from pathogens.
An explosion of research about our microbiome has found it can play a role in everything from how we respond to chemotherapy to our brain chemistry and immune response.
"When antibiotics were first developed and deployed, the overwhelming consideration was control of pathogens. We now realize that their widespread application has considerable collateral effect on the microbiome, which may be of special importance in developing children," the study said.
"Minimizing antibiotic use can be helpful to prevent antibiotic resistance, but there may be a role in preserving the microbiome based on this study," said pediatrician Dr. Jennifer Shu, author of "Baby and Child Health" and the American Academy of Pediatrics' "Heading Home with Your Newborn." Shu was not involved in the study.
"Of course, further studies would be needed to corroborate or refute these findings," she said, because it's unclear if the study's findings are "correlation or causation."