ERS: Air pollution shown to affect birthweight and level of childhood respiratory infections

18th September 2023

Three studies presented at the recent European Respiratory Society (ERS) International Congress in Milan, Italy, highlight the various damaging effects of air pollution in early childhood, including on birthweight and the incidence of respiratory infections.

According to a recent consensus statement from the European Respiratory Society on climate change, there is likely to be a disproportionately greater negative impact from global warming on individuals living with respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD).

One of the most important and detrimental consequences of climate change is the resulting increased levels of air pollution, which is already known to damage the lungs and have other negative consequences such as mental health issues in dementia.

Now, three related studies presented at the ERS International Congress have shed further light on the deleterious effect of air pollution. The studies reveal how pollution not only reduces the birthweight of newborns, but also increases the incidence of respiratory infections experienced by young children.

Effect on birthweight

In the first study (abstract PA311), researchers sought to investigate the association of maternal exposure to air pollution based on what they described as the level of environmental ‘greenness’ during pregnancy, and whether this affected birthweight.

They devised a measure of greenness termed the ‘normalised difference vegetation index‘ (NDVI), which was based on the density of vegetation seen on satellite images. In addition, the team modelled exposure to five known pollutants: nitrogen dioxide (NO₂), ozone, black carbon (BC), and two types of particulate matter (PM2.5 and PM10). The levels of these pollutants were estimated for mothers based on their residential address during pregnancy.

The researchers analysed data on 5,434 children from 2,742 mothers. The median NDVI_300m was 0.3 (interquartile range, IQR, 0.2 – 0.4). Increases in the level of greenness were positively associated with birthweight. For example, each IQR increase in NDVI_300m was associated with an increase in birthweight of 29g, a 23% lower odds of a low birthweight (Odds ratio, OR = 0.77, 95% CI 0.64 – 0.94), as well as a 14% increased odds of a high birthweight (> 4000g) (OR = 1.14, 95% CI 1.02 – 1.26).

Commenting on the findings, lead author, Robin Mzati Sinsamala, a researcher in the department of global public health and primary care at the University of Bergen (UiB), Norway said: ‘The time when babies are growing in the womb is critical for lung development. We know that babies with lower birthweight are susceptible to chest infections, and this can lead on to problems like asthma and COPD later on.

‘Our results suggest that pregnant women exposed to air pollution, even at relatively low levels, give birth to smaller babies. They also suggest that living in a greener area could help counteract this effect. It could be that green areas tend to have lower traffic or that plants help to clear the air of pollution, or green areas may mean it’s easier for pregnant women to be physically active.’

Air pollution and respiratory infections

In the second study (abstract PA311), which was published in the journal Pediatric Pulmonology, a UK team from Sussex Medical School and University Hospitals Sussex NHS Foundation Trust sought to evaluate the effect of environmental factors on respiratory infections and symptoms in early childhood.

Researchers turned to data from the GO-CHILD prospective birth cohort study, which explored the role of environment and gene variation on infection and atopy-related outcomes. As part of the study, pregnant women were recruited and their children followed up for infection and respiratory symptoms and outcomes after 12 and 24 months via postal questionnaires.

Information was available for 1,344 children, and the researchers identified how several environmental factors and settings were significantly associated with respiratory infections. For example, use of daycare facilities was associated with a more than two-fold increased risk of pneumonia (odds ratio, OR = 2.39), wheeze (OR = 2.16) and a dry cough (OR = 2.01). There was also a higher risk of developing bronchiolitis (OR = 1.40).

The presence of visible damp in the home increased the risk of wheeze (OR = 1.85) and led to a two-fold increased risk of being prescribed an inhaled corticosteroid (Relative risk, RR = 2.61).

Air pollution also contributed to the risk of respiratory problems. The presence of dense traffic around the child’s home, increased the risk of bronchiolitis (OR = 1.32). However, it was found that the harmful effects of environmental pollution could be mitigated to some extent by measures such as breastfeeding. In fact, continuing to breastfeed beyond six months was associated with a significantly reduced odds of bronchiolitis (OR = 0.55).

Commenting on this study, lead author, Dr Tom Ruffles from the Sussex Medical School, said: ‘This research provides some important evidence about how we can help reduce chest infections in babies and toddlers. The benefits of breastfeeding are well-established, and we should continue to support mothers who want to breastfeed their babies. We should also be making every effort to reduce exposure to infections in daycare, keep homes free of damp and mould, reduce tobacco smoking and cut air pollution.’

Rural versus urban location

Finally, researchers in the third study (abstract PA2721), who were part of the Copenhagen Prospective Studies on Asthma in Childhood (COPSAC) based at Gentofte Hospital and the University of Copenhagen in Denmark, looked at the level of respiratory infections seen in children who had been born in either a rural or urban location.

Using the COPSAC₂₀₁₀ mother-child cohort, researchers followed the participants from pregnancy until three years of age and recorded whether the children were growing up in urban or rural areas and how many respiratory infections they developed. The researchers also performed an analysis of the airway immune profile in the children at age four weeks and undertook both maternal and child metabolomic profiling during week 24 of their pregnancy and two to three days after birth.

Among 663 children, the team found there was a mean of 16.3 infections, which were mainly respiratory in nature. Among children living in an urban area, there was a 15% higher risk of infections compared to those living in rural areas (adjusted incidence rate ratio = 1.15, 95% CI 1.05 – 1.26, p = 0.002).

Urbanisation resulted in a different airway immune profile and it was this change that increased the risk of infections, they concluded. Furthermore, urbanisation resulted in different maternal and child metabolomic profiles, which significantly increased the risk of infections.

Lead author for the study and COPSAC researcher and physician, Dr Nicklas Brustad, said: ‘Our findings suggest that urban living is an independent risk factor for developing infections in early life when taking account of several related factors such as exposure to air pollution and starting day care. Interestingly, changes in the blood of pregnant mothers and newborn babies, as well as changes in the newborn immune system, seem to partly explain this relationship.

‘Our results suggest that the environment children live in can have an effect on their developing immune system before they are exposed to coughs and colds. We continue to investigate why some otherwise healthy children are more prone to infections than others and what the implications are for later health.

‘We have several other studies planned that will look for risk factors and try to explain the underlying mechanisms using our large amount of data.’