Miami, United States: Children at high risk of getting asthma may be missing some important gut bacteria in their first few months of life, according to a study Wednesday that helps explain why asthma is on the rise.

Cases of asthma -- a lifelong condition that causes wheezing, coughing and difficulty breathing -- have risen sharply since the 1950s, particularly in Western countries where up to 20 percent of children are affected, experts say.

But the cases have not climbed in the developing world. That has raised concerns that environmental factors or the trappings of modern life -- such as higher rates of Caesarean births, reliance on formula to feed babies rather than breastfeeding, overuse of antibiotics, or other factors -- may be to blame.

While scientists still do not have a definitive answer, the findings in the journal Science Translational Medicine identified for the first time four specific bacteria that appear to protect the immune system against asthma.

"This research supports the hygiene hypothesis that we're making our environment too clean," said study co-author Brett Finlay, professor of microbiology and immunology at the University of British Columbia. 

"It shows that gut bacteria play a role in asthma, but it is early in life when the baby's immune system is being established."
 
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The study involved more than 300 children whose stool samples were tested at age three months and one year.

The samples showed lower levels of four specific gut bacteria in three-month-old infants who were at an increased risk for asthma.

When fecal samples were studied at age one, there were fewer differences among the children, suggesting that the first 100 days of life is a critical window for a baby's developing immune system.

As years passed, 22 children with less diverse gut bacteria were tracked, and eight of them developed asthma. The rest of the group was considered at higher risk of asthma than other children in the study.

But it remains unclear exactly how infants acquire these particular bacteria -- they are named Faecalibacterium, Lachnospira, Veillonella and Rothia -- and researchers said more study is needed to find out why some babies naturally acquired them from their environments and others did not.

"We know very little about them," co-author Marie-Claire Arrieta of the University of British Columbia told reporters. 

"There are known inhabitants of different parts of our gastrointestinal tract, but we're just starting to do analysis to learn more about them."

None of the 22 children at high risk for asthma were treated with antibiotics in the first months of life, ruling that out as a potential cause for the less diverse bacteria.

But the researchers also said they did not examine the children's mothers for the same bacteria, nor did they examine whether birth vaginally or by C-section, or bottle versus breastfeeding, could have played a role -- though these are directions for future study. 

"This study, I think, maybe starts to emphasize that we need to revisit our relationship with bacteria," said co-author Stuart Turvey, a doctor at the British Columbia Children's Hospital, who cautioned against seeking the answer in store-bought products.

"We're starting to discover this massive universe of bacteria," said Turvey.

"And the bacteria that are often presented in the probiotics we can buy at the health food store or the supermarket are just one small handful of bacteria, and certainly don't include this flavor combination that we've identified."