Asthma is one of the most common diseases in the developed world, but its causes remain shrouded in mystery. A new study by Canadian scientists suggests four specific bacteria may play a role, however — and that babies have a “critical window” during which disturbances in their gut microbes can have lifelong consequences.
Published Wednesday in Science Translational Medicine, the study is the latest to mine the mysteries of the microbiome, the trillions of microbes that call the human body home.
Analyzing the stool of 319 Canadian infants, researchers found that kids with the highest risk of developing asthma had low or non-existent levels of four specific bacteria.
But this difference, observed at 3 months, largely disappeared by the time the kids turned 1. This suggests the “first 100 days of life represent an early-life critical window,” during which changes to the gut bacteria could influence a baby’s risk of developing asthma, according to the study.
“I think it’s quite exciting and a very important paper,” said asthma researcher Marsha Wills-Karp, an environmental health sciences chair and professor with Johns Hopkins University, who was not involved with the study. “Other papers have looked at pieces of this puzzle, but this one is putting the puzzle together.”
An explosion of research in recent years has deepened our understanding of the microbiome’s importance in shaping human health. Scientists are now linking disturbances in our microbial communities to everything from obesity and malnutrition to cancer and acne.
Emerging evidence suggests the microbiome could also be playing a role in asthma, a chronic lung disease that affects more than 300 million people worldwide.
While some people are genetically predisposed to asthma, scientists believe environmental factors are also to blame. Asthma rates have risen sharply in the developed world but not in poorer countries — perhaps because wealthier countries have higher rates of Caesarean sections and antibiotic use, both of which alter the gut microbiome and have been linked to asthma, according to Dr. Brett Finlay, a microbiologist with the University of British Columbia and the study’s senior author.
“There’s all these smoking guns to indicate that the microbiota might be involved,” Finlay said Tuesday in a telephone conference. “But there were no experiments to prove it.”
So Finlay and his team conducted experiments in lab mice to show that early changes in the gut microbiome can lead to higher asthma risk.
This latest study, however, tests whether the same might be true for humans. Analyzing fecal samples from babies from Vancouver, Edmonton, Manitoba and Toronto, the researchers found that children treated with antibiotics before the age of 1 were more likely to have increased asthma risk.
The 22 infants with the highest asthma risk were also missing microbes found in the guts of healthier kids: Lachnospira, Veillonella, Faecalibacterium, and Rothia, known collectively as FLVR.
It appears that these four bacteria could be protective against asthma, Finlay said. But they were only missing in stool samples taken at 3 months of age. When researchers again tested the stool at the end of the babies’ first year, the microbial differences were much less apparent.
“In that first 100 days, the structure of the gut microbiome seems to be very important in influencing the immune responses that cause or protect us from asthma,” said study co-author Dr. Stuart Turvey, a pediatric immunologist with B.C. Children’s Hospital. “That very early life window is critical.”
To demonstrate that these microbes have a protective effect, the researchers implanted the FLVR bacteria into laboratory mice that had ingested feces from an asthmatic child. These mice had significantly reduced airway inflammation and asthma risk compared to mice without the FLVR bacteria, the study found.
Much more research is needed before conclusions can be drawn about the microbiome’s precise role in asthma. This study will also have to be replicated to test whether these findings hold true in other populations.
But Finlay hopes his research will eventually help identify at-risk kids or lead to treatments for preventing asthma. He said his study also highlights an important public health message.
“We need to revisit our relationship with bacteria. The clinical relationship has often been ‘Bacteria is bad and we should kill them with antibiotics,’” he said. “But this study and others like it emphasize that we’ve evolved with bacteria and they’re really important for our health.”
334 million: Approximate number of people who have asthma worldwide
3 million: Approximate number of Canadians who have asthma
14: Per cent of the world’s children who experience asthma symptoms
15.6: Per cent of Canadians between 4 and 11 diagnosed with asthma
250: Estimated number of Canadians that die every year from asthma
Sources: Global Asthma Report 2014, Asthma Society of Canada