Babies and young children with diverse bacteria in their gut are less likely to develop allergy-related wheezing and asthma, according to a new Australian study.

Communities of bacteria, known as microbiota, develop in the human body during the early years of life and are involved in processes that are helpful to the body, such as synthesizing vitamins and boosting the immune system. They can also be occasionally unhelpful, due to the role they play in inflammatory bowel disease and stomach ulcers.

Babies already have some microbiota in their guts from their mothers when they are born. The diversity of bacteria then increases and matures as they are exposed to other children, animals, and different foods.

The researchers analyzed data from the Barwon Infant Study (BIS), which has been running in Australia since 2010, watching 1,074 babies as they grow.

The new results showed that a more mature infant gut microbiota at one year of age was associated with a lower chance of developing food allergies and asthma in childhood.

"This appeared to be driven by the overall composition of the gut microbiota rather than specific bacteria," said Dr. Yuan Gao, a research fellow at Deakin University, in Geelong, Australia, who presented the study this week at the European Respiratory Society International Congress in Milan, Italy.

They tested whether maturation of the infant gut microbiota in early life is associated with decreased risk of allergy-related wheeze in later childhood—and found they were essentially correct.

For this current study, Dr. Gao and her colleagues looked at the bacteria present in fecal samples collected from the BIS babies one month after birth, six months and one year. At the one-year and four-year postnatal reviews, the BIS investigators asked the parents to report on whether their children had developed allergy-related wheeze or asthma in the previous 12 months. They also did skin-prick tests to see if the children had allergic reactions to any of ten foods and any airborne substances that can trigger an allergic response, such as rye grass or dust.

In a randomly selected sub-group of 323 children, the BIS team used a DNA sequencing technique to identify and characterize the gut microbiota. They calculated ‘microbiota-by-age z-score' (MAZs), which is a mathematical estimate of the maturity of the children's gut microbiota.

"We found that if babies had more mature gut microbiota when they were one year old, they were less likely to have an allergy-related wheeze at one and four years old," said Dr. Gao. "If MAZ increased within a certain range, known as standard deviation, it halved the risk of allergy-related wheeze at both these ages."

The mechanisms by which mature gut microbiota contribute to preventing allergy-related disease is not completely understood. "Given the complex origins and development of both gut microbiota and the infant immune system, it is likely that the protective effect of a healthy gut microbiota occurs as a result of communities of bacteria acting in multiple different ways, rather than via one particular mechanism," said Dr. Gao.

"We hope that by understanding how the gut microbiota improves the immune system, new ways of preventing allergy-related disease such as asthma can be developed.

The researchers are planning to recruit 2000 children from Australia and New Zealand to a new clinical trial, called ARROW, to see whether giving young children a mixture of dead bacteria, taken orally, can protect them from wheezing illnesses or asthma by boosting a healthy immune response to viral infections. Viruses are the commonest causes of childhood illnesses and can lead to chest infections and wheezing.

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"ARROW has the potential to dramatically improve the health of children with recurrent wheeze and asthma," said Dr. Gao.

Strengths of the study include its design, which allowed researchers to analyze the development of gut microbiota as the children grew older, and also the fact that the BIS children were drawn from the general population. Limitations include the fact that the DNA methods used to characterize the gut microbiota cannot provide insights into the function of the bacteria.

Dr. Erol Gaillard, a pediatric respiratory expert in the UK who was not involved with the research guessed that the rising incidence of allergy-related illnesses like asthma and eczema may be due to less diverse foods eaten at an early age and less exposure to farm animals.

"Exposure to a variety of bacteria from an early age is very likely if babies and children are regularly mixing with other children and animals and are exposed to a larger variety of foods. If we can find ways to boost the maturity of gut microbiota, this could have a significant effect on the incidence of allergies, and so it will be interesting to see the results of the ARROW study."

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