Moisture, mould and the farm effect: decoding how indoor environments affect respiratory health

Diet and lifestyle 5. dec 2023 2 min Former researcher Amélie Keller Written by Morten Busch

Researchers explored how indoor environments affect children’s respiratory health by using the Danish National Birth Cohort and discovered patterns. The new study identifies different types of important exposure and examines how they are associated with the development of asthma in adolescence. The findings emphasise the importance of household characteristics, including moisture, mould, living in a farmhouse and pet ownership. The research delves into indoor air quality complexities and highlights possible interventions to improve public health.

The focus on indoor air pollution is gaining prominence in respiratory health. Outdoor air pollution has long been studied, but how indoor air quality affects well-being, especially during childhood, is now being scrutinised. A novel study based on the Danish National Birth Cohort investigated the pivotal role of indoor environments in shaping respiratory health.

“Children in Denmark and other temperate climates spend much of their time indoors, and understanding the intricate links between indoor air quality and asthma therefore becomes paramount. There have been many studies on outdoor air pollution over the past year, and I think the focus on indoor air pollution is quite recent compared with outdoor air pollution. However, the knowledge that indoor air, like outdoor air, has substantial health impacts, is gaining attention,” explains Amélie Keller, lead author and former researcher at the Department of Public Health of the University of Copenhagen.

Exposure before birth

The new study is based on data from the Danish National Birth Cohort led by Anne-Marie Nybo Andersen – a groundbreaking cohort initiated in 1996 and encompassing more than 100,000 pregnancies to investigate the causal link between exposure in early life and disease later on and the possibilities for preventing disease. The new study focused on children from the Cohort aged 11–18 years – using latent class analysis.

“This method identifies clusters of individuals with shared exposure profiles, recognising the complexity of real-life exposure in which multiple pollutants coexist, unlike traditional analysis, which focuses on a single exposure. The findings reveal five latent classes, each representing distinct patterns of exposure to indoor home characteristics,” says Amélie Keller.

The probability of having asthma at 18 years of age was highest among individuals in a class with higher clustering on household dampness.

“Our study hints at the prolonged impact of exposure from before birth. Unlike certain types of exposure at age 10 years, exposure during pregnancy and early childhood is more substantially associated with the risk of developing asthma. This emphasises how moisture and mould can potentially harm respiratory health,” explains Amélie Keller.

A key protective farm factor

The study also reveals protective factors – adolescents who grew up in farmhouses or were exposed to dogs or cats indoors demonstrated a lower risk of asthma at age 18 years. The farm effect and the presence of dogs or cats indoors seem to contribute to a lower risk of asthma. Nevertheless, some of this effect may also result from other factors more prevalent in rural environments (such as natural surroundings and population density), since earlier research based on the Danish National Birth Cohort showed no protective effect of exposure to livestock.

“Our study adds to the existing literature that living in a farm environment is protective. Studies also suggest that exposure to pets may generally be more beneficial for those without a family history of asthma. And again, unlike exposure to a cat at age 10 years, exposure during pregnancy and early childhood may more substantially influence the risk of developing asthma,” says Amélie Keller.

Since the findings are solely based on epidemiological data, they cannot provide any decisive explanation for the biological mechanisms, but they clearly highlight the importance of considering multiple type of exposure simultaneously.

“The study identifies moisture as a negative factor and farm living and dogs and cats as positive factors and thereby paves the way for targeted interventions and the role of housing in public health strategies for preventing asthma,” explains Amélie Keller.

Data are instrumental in unravelling the mysteries

It is still too early to gauge the impact of this research.

“The project is wrapping up, and we have published several articles. The upcoming one focuses on residential exposure to mould, dampness, particle pollution and the risk of respiratory tract infections,” continues Amélie Keller.

The wealth of accessible data in Denmark proves instrumental in unravelling the mysteries of respiratory well-being, offering valuable insights for global health initiatives. The Danish National Birth Cohort is one of the largest birth cohorts with long-term follow-up globally and highlights Denmark’s wealth of accessible data.

“The new study reflects the complexity of real-life exposure, acknowledging the multifaceted nature of respiratory risks,” concludes Amélie Keller.

Exposure to different residential indoor characteristics during childhood and asthma in adolescence: a latent class analysis of the Danish National Birth Cohort” has been published in the European Journal of Epidemiology. The Danish National Birth Cohort was established with a substantial grant from the Danish National Research Foundation and funding from Denmark’s regional councils, the Pharmacy Foundation, the Egmont Foundation, the March of Dimes Birth Defects Foundation, the Health Foundation and other minor grants. The study was also funded by the Danish Medical Research Council, Innovation Fund Denmark, the Nordea Foundation, Aarhus Ideas, University of Copenhagen Strategic Grant and the Danish Council for Independent Research. The Lundbeck Foundation and the Novo Nordisk Foundation supported the Danish National Birth Cohort Biobank used for the study . This study was made possible by a grant from the Realdania Foundation. The funders of the study had no role in the design, analysis or interpretation of the study and were not involved in the decision to publish.

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