Asthma

Asthma and the gut, from infancy onward

Multiple layers of evidence, from human infants to laboratory mice, point to a real gut connection in early-life asthma risk. Asthma is the most common long-term illness in children, affecting more than 14% of children worldwide. Babies who went on to develop asthma had lower levels of four specific gut bacteria, nicknamed FLVR, at just three months old, according to a study following 319 infants in the Canadian CHILD birth cohort. FLVR stands for Faecalibacterium and Lachnospira, plus Veillonella and Rothia, four bacteria most babies pick up naturally from their environment. Researchers had first identified 22 infants in the cohort as being at high risk of asthma, based on allergy testing and a tendency to wheeze, and it was this small group that showed the clearest FLVR shortfall. These infants also had lower levels of the beneficial compounds those bacteria normally produce. Researchers then gave the missing FLVR bacteria to newborn mice. The mice went on to develop less severe asthma-like symptoms, direct experimental support for a link the human data could only show as an association.

Source: PMC, The role of the early-life gut microbiome in childhood asthma

A clinical trial shows a measurable effect

A double-blind, placebo-controlled trial in adults with allergic asthma tested a synbiotic supplement, a combination of live bacteria and the fibre that feeds them. Taking the synbiotic significantly improved peak expiratory flow, a measure of how forcefully a person can breathe out, both in the morning and evening compared with a placebo. The trial found no change in airway hyperresponsiveness, a measure of how reactive the airways are to triggers, but the improvement in day-to-day breathing was real and measurable over four weeks of use.

As with any probiotic or synbiotic, adding bacteria on its own is not the whole story. Newly introduced microbes need an ongoing food supply, fibre and plant compounds, to establish themselves rather than dying back out. It is the same reason a zoo needs to keep feeding any new animals it brings in, not just add more of them.

Source: Allergy, Synbiotics reduce allergen-induced T-helper 2 response and improve peak expiratory flow in allergic asthmatics

The picture beyond childhood

The picture is more mixed once childhood is over. A UK study found adults with asthma had a less rich gut microbiome than healthy adults, with several beneficial bacteria, including Faecalibacterium prausnitzii, notably depleted. A much larger Dutch study included 1,632 adults, 172 of whom had asthma. It found no significant link between gut bacteria and adult asthma once other factors were accounted for. That contrast suggests the gut's influence may matter most in early life, while the immune system is still developing, rather than acting as a continuous driver once asthma is already established.

Gut bacteria produce short-chain fatty acids, chemical compounds made when fibre is fermented in the gut. In mice, giving these compounds directly reduced airway inflammation driven by specific immune cells, even when the mice were exposed to substances that normally trigger an asthma-like reaction. This gives a plausible mechanism for why gut bacteria might matter more for some people's asthma than others, depending on how much of these compounds their gut produces.

Source: PMC, A metagenome-wide association study of gut microbiota in asthma in UK adults

Source: PMC, Dietary Fiber-Induced Microbial Short Chain Fatty Acids Suppress ILC2-Dependent Airway Inflammation

What this means for you

Asthma needs proper diagnosis and an ongoing treatment plan from a doctor, especially in children, where the evidence for a gut connection is currently strongest. Sudden severe breathlessness, blue-tinged lips, or a rapidly worsening attack need emergency medical care. The trial evidence on synbiotics and breathing, and the mouse studies confirming a causal role for specific bacteria in early life, are real reasons to support the gut alongside medication. That means offering a wide variety of plant foods and fibre sources from infancy onward, since fibre is what lets FLVR bacteria and others like them keep producing the compounds this research links to calmer airways. Fermented foods such as yoghurt can be a useful addition too, if they are well tolerated. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.