Wheezing: Can breastfeeding for longer make a difference?

Public health bodies put a lot of effort into encouraging mothers to breastfeed, and for good reasons. Successive studies have shown breastfeeding has a range of health benefits, including a lower risk of wheezing illnesses, which can be linked to asthma. But which of these illnesses are most likely to respond? Is a breastfed child less likely to develop wheezing after age five, or age seven, for instance? Or is the protective effect mainly measurable only in younger children? Professor Maria Quigley from the National Perinatal Epidemiology Unit at the University of Oxford, along with colleagues at Oxford and UCL, has been looking at how and when breastfeeding is associated with wheezing.

Asthma is the most common chronic condition affecting children and young people in the UK. It’s the most common reason why children are admitted to hospital, and sadly each year a few still die from the condition. According to the British Lung Foundation three children in every hundred under the age of five have been diagnosed with asthma at some point; and by age 10 that figure rises to one in 10.

There’s no cure, and so the priority for public health bodies has been to understand the disease better, to manage it better and to learn more about the factors that can protect us from it. One such protective factor is breastfeeding: two recent pieces of research have shown there is a lower risk among breastfed children, but that the effect is stronger among the very young – both for asthma and for wheezing, which has many causes and which does not necessarily develop into asthma.

Childhood wheezing can follow a variety of patterns – it can set in early but clear up before adulthood, for instance, or it can start later but continue into later life. Some wheezing will start in childhood and will continue.

Millennium Cohort Study

We wanted to look at how breastfeeding might affect these different types, so we used data from the Millennium Cohort Study, which has followed the lives of almost 19,000 children born in the UK between September 2000 and January 2002. Their parents were interviewed when they were 9 months old, and again when they were 3, 5, 7 and 11 years.

Our study focused on just over 10,000 children who were seen at all of those points and who were the product of single as opposed to multiple birth. Mothers were asked whether they had tried to breastfeed, and for how long their children had been breastfed.

Among our sample, seven out of 10 children had been breastfed: a little more than one in ten of the study sample for less than a week; a fifth for between one and three weeks, just over one in six for three to six months and around a quarter for six to nine months.

We found that at age 9 months, 6.5 per cent of children had a history of wheezing. At age 3 years, 19.5 per cent had such a history in the past year. As the children got older, though, this proportion decreased – 16 per cent at age five, 11.8 per cent at age seven and 11.4 per cent at age 11.

Overall, 37 per cent of children had suffered from wheezing at least once between 9 months and 11 years. A little under a fifth (18.8 per cent) had wheezing at younger age which cleared up when they got older, while 6.2 per cent had wheezing which started later and 11.8 per cent had persistent wheezing.

Feeding and wheezing

When we looked at the association between breastfeeding and wheezing, we found the children who had been breastfed for longest were less likely to suffer from wheezing.

But this effect lessened with time. For example, those breastfed for six to nine months were less likely to wheeze between the ages of nine months and five years, but by the age of 11 this group had no significant advantage over those who were breastfed for less time.

What does our study tell us about the relationship between breastfeeding and wheezing? The picture is a complex one. There are many causes of wheezing and of asthma, and those causes change over time. So in order to draw firm conclusions about cause and effect, we would need a much more complex dataset. It would be interesting, for instance, to look at clinical information on children’s allergies or their lung function.

But what we can say is that age matters – in order to understand how breastfeeding affects the development of wheezing during childhood, we must take a longer and more nuanced view.

Breastfeeding And Childhood Wheeze: Age-Specific Analyses and Longitudinal Wheezing Phenotypes as Complementary Approaches To The Analysis Of Cohort Data is research by Maria Quigley (University of Oxford), Claire Carson (University of Oxford) and Yvonne Kelly (UCL). It is published in the American Journal of Epidemiology.