July 6, 2017

expert reaction to study investigating the association between maternal consumption of sugar and childhood allergies and allergic asthma

Publishing in European Respiratory Journal scientists investigate the association between childhood asthma and allergies and maternal consumption of sugar.

Dr Rahul Chodhari, Consultant Paediatrician, Royal Free London Foundations NHS Trust, & spokesperson for the Royal College of Paediatrics and Child Health (RCPCH), said:

“We know that maternal health and wellbeing has a profound impact on child health and this is impacted upon by a variety of factors, such as smoking and weight during pregnancy. Whilst links between asthma and high levels of sugar consumption by children have been suggested before, this is the first study to identify a potential association between sugar intake in pregnancy and allergy or allergic asthma in children and, as such, it is very interesting.

“The ALSPAC is a strong population-based birth cohort resource with a fairly large sample size. However, most births in the cohort took place before we saw significant rises in atopy rates among children and the period of this study misses potential improvements in lowering sugar intake that we might have made through public health campaigns more generally. In addition, measuring sugar intake can be difficult with ethnic variations in food types consumed and how sugars are processed. And we know that there are multiple factors associated with increased allergic disorders, such as long food chains, lack of exposure to common infections and pollution to name just a few.

“We must therefore interpret the study’s findings very carefully and further research is needed to prove the association before changes to health policy can be supported. In the meantime, pregnant women should follow the current guidelines which recommend a diverse diet in moderation and that weight-gain be monitored closely.”

Prof. Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“This is a good, careful study carried out on substantial numbers of parents and children, but it’s important not to make too much of it. The authors describe several important caveats (in the paper and in the media release).

“This is an observational study, and no single study of this kind can establish what does or doesn’t cause a disease. The researchers found that children, whose mothers said they had eaten larger amounts of sugar during pregnancy, were more likely to have certain types of allergy and asthma, than children whose mothers said they had eaten less sugar when they were pregnant. But it doesn’t tell us that it was the extra sugar that caused the children’s allergies. Perhaps the mothers who ate more sugar had diets that were different in other ways from the mothers who ate less sugar, or perhaps they had different smoking habits, for instance. Perhaps it was these other aspects of diet, or smoking, that caused their children’s allergies and asthma, and not the sugar. It’s possible to allow statistically for such differences (confounders, in the jargon) if you have data on them, but even then these statistical adjustments may not work perfectly. In fact these researchers did allow for an impressively long list of possible confounders in their statistical analysis, but as the paper and the media release make clear, we still can’t by any means be certain that the children’s asthma or allergies were caused by their mothers’ sugar eating habits during pregnancy. The researchers do describe a biological way by which a mother eating sugar during pregnancy could affect whether their child develops asthma or an allergy, but they correctly point out that this aspect of the study is speculation – it’s possible that things work like that, but it’s also perfectly possible that they don’t.

“Because one observational study can’t establish the causes of a disease, evidence for a cause needs to be put together from several studies. Therefore I welcome the researchers’ suggestion that they look at a different cohort of mothers and children to see if the relationship can be seen there too, and then possibly to do a randomised controlled trial to investigate further. Only after this kind of further work might we come near to knowing whether or not the mother’s sugar eating really increases the risk of asthma and allergies in her children.

“It’s important to realise that the study report found strong evidence of a correlation between sugar consumption in pregnancy and children’s disease only for some of the types of asthma and allergy that they considered. The strong evidence was for children allergic to two or more allergens (of the three they tested for, dust mites, cats and grass), and for children with allergic asthma. But both of these conditions are quite common. In the group they studied, at around the age of 7, about 9 in every 100 children (about 1 in every 12) was allergic to two or more allergens, and about 6 in every 100 (about 1 in 16) had allergic asthma. (Some children will have had both conditions.) So, if higher sugar consumption by pregnant mothers is shown in further studies to be a cause of these conditions, changing sugar consumption could have quite a substantial effect on the numbers of children with several allergies and allergic asthma.”

Dr Sheena Cruickshank, Senior Lecturer in Immunology, University of Manchester, & British Society for Immunology representative, said:

“This study represents a lot of work on a large dataset. The paper reports a small association between maternal free sugar intake during pregnancy and the occurrence of allergy or allergic asthma in the children at 7 years of age. From these findings, it is unclear how strong this effect is.  These results also only show an association between allergy and high maternal sugar intake during pregnancy; more studies will be needed to work out if there is any causation in this relationship.

“Atopic diseases, such as allergy and asthma, are complex and associated with many genetic and environmental effects, including the microbes and pollutants we are exposed to.  Several studies have also suggested the microbiome (the community of microbes that live in and on us) is altered in allergy and it is well established that the child’s microbiome is influenced by how a baby is delivered, the type of milk the baby is fed as well as their diet as they grow older and thus there may be indirect effects via the microbiota.  Future studies should look to take these variables into account so we can understand the full relationship between maternal diet during pregnancy and allergic disease in the offspring.”

* ‘Maternal intake of sugar during pregnancy and childhood respiratory and atopic outcomes’ by Bédard et al. published in European Respiratory Journal on Thursday 6 July. 

Declared interests

Dr Sheena Cruickshank: No conflicts of interest.