Pregnancy and child

A baby's gut bacteria 'could influence allergy risk'

"Feeding infants good bacteria 'can slash their risk of getting asthma'," is the Mail Online's entirely speculative headline.

The study the news comes from did find a link between certain patterns of gut bacteria and fungi and subsequent asthma risk, but it is unclear how that risk can be reduced.

Stool samples from 130 one-month-old babies were analysed according to the amount and type of bacteria and fungi they contained.

Based on the analysis, the samples were then grouped into three categories: neonatal gut microbiota (NGM) 1, NGM 2 and NGM 3.

The study found children at higher risk of allergies and asthma had lower amounts of important bacteria in their gut, and higher levels of certain fungi – these children made up the NGM 3 group.

But this research has limitations, the main one being that the study is not able to prove that low levels of "good" bacteria in the gut causes allergies. The research can only provide a link that needs to be studied further.

In addition, the main results are based on the NGM 3 group, which contained just 11 infants who were deemed to be at a higher risk.

This study did not look at any methods that might be used to change gut microbes and the subsequent potential impact on allergy risk.

Currently, the only proven method to reduce the risk of childhood allergies in later life is breastfeeding.

Where did the story come from?

The study was carried out by researchers from a number of institutions, including the University of California, the Department of Public Health Sciences in Detroit, and the University of Michigan Medical School. 

Funding was provided by the US National Institutes of Health, the National Institute of Allergy and Infectious Diseases, and the Alfred P Sloan Foundation.

The study was published in the peer-reviewed journal, Nature Medicine.

Some of the Mail Online's reporting is not supported by the evidence presented in the study.

Saying "Feeding infants good bacteria 'can slash their risk of getting asthma'," while arguably plausible, is not backed up by the evidence presented in the research. The study did not look at the use of "friendly bacteria", also known as probiotics.

The Guardian took a more cautious tone and quoted an independent expert, Professor William Cookson, who highlighted the small number of children in the high-risk NGM3 group. 

He also remarked: "Asthma is a disease of the airways, it is not a disease of the bowel, and the airways have their own microbiota – fungi and bacteria – which are very, very plainly abnormal in asthmatics. So the more logical thing to do, to me, is to look at the lungs, rather than to look at the bowels." 

What kind of research was this?

This cohort study aimed to assess the link between levels of microbes in the gut and the risk of childhood allergies and asthma. 

While this study is able to provide links for further investigation, it is not able to prove the microbes are responsible for the allergies seen.

However, in this case the evidence provided is in agreement with the large body of evidence that says bacteria in the gut can influence health in many different ways.

What did the research involve?

Pregnant women aged between 21 and 49 were recruited from August 2003 to November 2007 as part of the Wayne County Health, Environment, Allergy and Asthma Longitudinal Study.

This was a prospective birth cohort study designed to investigate early life risk factors for allergic diseases.

Five follow-up interviews were conducted 1, 6, 12, 24 and 48 months after the birth of the children. Stool samples were collected from the children at the one- and six-month home visits.

The study only included children who had completed their 24-month visit.

This also involved taking a blood sample so antibodies related to the immune system's response to an allergen could be measured.

Dust samples were collected from their homes at the same time as the stool sample.

What were the basic results? 

Stool samples from 130 newborns with an average age of 35 days were analysed and divided into three states based on the levels of bacteria found. These were neonatal gut microbiota (NGM) 1 to 3.

Each state was found to be associated with a different risk of allergy at two years of age and asthma at four years of age.

The NGM3 group was found to be at an almost three times higher risk than the NGM1 group for allergy, (relative risk [RR] 2.94, 95% confidence interval [CI] 1.42 to 6.09) and asthma (RR 2.95, 95% CI 1.09 to 7.98).

The high-risk NGM3 group were found to have lower levels of certain "good" bacteria, such as bifidobacterium and faecalibacterium, and higher levels of fungi, such as candida.

No statistically significant difference in risk was seen between NGM1 and NGM2 for allergy or asthma.

The number of infants in each group was small. There were just 11 infants in the NGM3 group, four of whom developed asthma, compared with five out of 49 infants in NGM2 and eight out of 70 infants in NGM1.

How did the researchers interpret the results?

The researchers concluded that their findings show microbes found in the newborn gut influences susceptibility to childhood allergic asthma, potentially via alterations in the gut microenvironment.

They suggest that very early life interventions could be used to manipulate the composition and function of the gut microbiome, and might offer a viable strategy for disease prevention.


This cohort study aimed to assess the link between levels of microbes in the gut and the risk of childhood allergy and asthma.

The study found children with lower amounts of important bacteria in their gut and higher levels of certain fungi were at an increased risk of allergy and asthma. 

Microbes such as bacteria and fungi are passed from mothers to babies during birth, as well as while breastfeeding and from the environment.

This finding is in agreement with the large body of evidence on the importance of "good" bacteria in the gut and the positive influence on health outcomes.

But this research has limitations:

  • Because of its design, the study is not able to prove that the microbes in the gut are causing the allergies – it can only provide a link to be studied in further research.
  • The number of stool samples examined was quite small, and the significant findings were based on a very small number of participants in the NGM3 group, so it is possible the effect seen is the result of chance.
  • It is not clear whether, or to what extent, exposure to other risk factors for allergy and asthma were taken into account in the analysis.

The study's authors mention that this may be one cause of allergy and asthma, but there are a number of other potential causes that have not been addressed here.

This research has not looked at the effect of changing the type and level of gut microbes, so there is no backing for the Daily Mail's claim that "introducing mixtures of beneficial bacteria into the stomach of a baby at risk mean that they are less likely to develop allergies or asthma".

Probiotics for babies are now big business, but evidence of their benefits is not so big.

While there is some limited evidence probiotics may be of benefit in some very specific circumstances – such as preventing digestive conditions in premature babies – there is currently no credible evidence that they should be routinely used in healthy babies.

NHS Attribution