“Children at nursery less likely to get asthma”, reports The Daily Telegraph . Spending time with other youngsters from the age of six to 12 months “can cut the chance of developing the condition by 70%”, the newspaper says.
The study underlying this story offers some evidence that attendance at daycare may provide some protection against persistent wheeze (wheeze that is present in children before three years and still present in the 12 months prior to age five years). However, wheeze can occur for many reasons in childhood and it does not necessarily mean the child has asthma. Certainly more work will be needed to ascertain whether attendance at nursery (which is likely to mean exposure to more infections) itself is protective, or whether the population of children who attend nursery during their childhood is intrinsically different to the population which does not.
Where did the story come from?
Dr Nicolaos Nicolaou and colleagues from the University of Manchester carried out this research. The study was funded by Asthma UK and the Moulton Charitable Trust. The study was published in the peer-reviewed medical journal: Journal of Allergy and Clinical Immunology .
What kind of scientific study was this?
The study was a prospective cohort study enrolling children born at Wythenshawe Hospital, Manchester and Stepping Hill Hospital, Stockport, between January 1996 and April 1998. Participating children attended follow-up meetings at one, three and five years of age. During these follow-ups, information was collected on attendance at daycare, pets, socioeconomic status, exposure to tobacco smoke, childcare arrangements, number of siblings, symptoms, diagnosis and history of wheeze. At ages three and five, lung capacity was measured and, at age five, sensitivity to cats, dogs, grass, eggs, milk and mould was assessed using a skin-prick test.
The researchers explored the effect of various risk factors on whether or not the child had wheeze at age five years. Current wheeze was defined as the child having wheezing or whistling in the chest in the last 12 months. Children were then divided into groups: no wheezing (during the first three years of life), transient early wheezing (wheezing in the first three years but not since), late onset wheeze (no wheeze in first three years but wheeze in previous 12 months when questioned at five years) and persistent wheeze (wheeze during first three years and in previous 12 months). Although there were 1,085 children born into the cohort, full data was available for only 815 children.
What were the results of the study?
Of the 815 children, 439 of them had never wheezed, 201 were transient early wheezers, 47 were late-onset wheezers and 128 were persistent wheezers. The researchers found that entry into nursery between the ages of six and 12 months was independently linked with a reduced risk of current wheeze at five years of age (i.e. it was still statistically significant even after taking into account other factors such as exposure to tobacco smoke, maternal asthma etc.).
There was no link between daycare attendance and lung function, but daycare attendance between six and 12 months increased risk of atopy (hypersensitivity to certain allergens). Having older siblings also reduced the risk of rhinoconjunctivitis (runny nose and congestion). They note that maternal smoking, allergic sensitisation at age five years, male gender and maternal asthma were all predictors of current wheeze at age five years.
What interpretations did the researchers draw from these results?
The researchers conclude that children who attend nursery have a reduced risk of current wheeze at age five years compared with children cared for at home or by a child-minder. They note that the protective effect was greatest when children entered daycare when they were aged between six and 12 months.
What does the NHS Knowledge Service make of this study?
This longitudinal study provides some evidence for a link between attendance at daycare and reduced risk of persistent wheeze (defined as wheezing up to age three years and in the previous 12 months when questioned at five years). The researchers note some limitations to their study, including:
- The assessment of many of the risk factors relied on parental reporting. This may have meant some inaccurate classifications, particularly as parents were expected to remember presence of wheeze in their children up to five years in the past.
- An important limitation in this study is the number of children in the different subgroups. Only 41 children had started nursery in the first six months of life. The researchers suggest that the small sample size may explain the lack of significant protective effect of attendance in this group.
- The researchers used “attendance at daycare” as a proxy measure for exposure to many infectious agents – i.e. they did not directly measure “infections”. They cite research that has suggested that children attending daycare experience more infections than children do cared for at home.
- In some of their analyses, the researchers do not use multivariate modelling – i.e. they do not take into account the other factors that may be having an influence.
- Importantly, this study was considering associations with parental reported wheezing and not a medically confirmed diagnosis of asthma. Current wheezing was considered to be any wheeze or whistling in the chest in the past 12 months; many young children develop wheezing or whistling in the chest when they have an acute respiratory tract infection, but this does not mean that they have asthma. Diagnosis of asthma in children is always challenging and although wheezing may be the most well known symptom, there are others and wheeze may be absent altogether, e.g. in many children with asthma, nocturnal cough is the only symptom. It is worth noting that there was no association between nursery care and lung function tests.
The researchers note that previous studies investigating the relationship between attendance at daycare and wheeze have found conflicting results, particularly surrounding the age of effect. However, they say that their study suggests that attendance reduces the risk of asthma in all ages but is strongest in children who start nursery between six and 12 months. Given the limitations the authors highlight, more research is needed. In fact, the authors themselves suggest that, “further information is essential to ascertain whether the increasing trends in daycare attendance may act as a potential protective cofactor in preventing early childhood wheezing”.