Childhood Asthma and Polyunsaturated Fats
Australian research suggests that pre-school children taking a diet high in polyunsaturated fats are more likely to develop asthma.
Norman Swan:Australian research published internationally last week which suggested that pre-schoolchildren taking a diet high in polyunsaturated fats are more likely to suffer from asthma.
Dr Michelle Haby of the Royal Children's Hospital in Melbourne was the lead author.
Michelle Haby:We sampled pre-school age children aged 3 to 5, from two cities in New South Wales, Lismore, which is near the coast, and it's a humid city, and Wagga Wagga, which has a dry climate. There's no real register of pre-school age children, but we got them through pre-schools, childcare centres, immunisation records, family day care, and we asked their parents to fill in a questionnaire asking them about asthma symptoms, medications and their diet, siblings and other risk factors. We also went to these towns and skin-prick tested them, so that was to test whether they were allergic to common allergens.
The question about polyunsaturated fats was quite a simple one, what fats they used on bread and toast, and what ones they used for cooking. And if they used polyunsaturated fats for both, we classified them as having a high polyunsaturated fat intake. There was an association that showed that children who had a diet high in polyunsaturated fats had twice the risk of having asthma.
Norman Swan: And at what age, in terms of their eating, did it make a difference?
Michelle Haby: We only asked about what fats they currently use, so we can't speculate as to whether they've used those types of fats for the whole of the child's life.
Norman Swan: So what factors predicted a lower risk of asthma?
Michelle Haby: Breast-feeding and having three or more older siblings.
Norman Swan: Having three or more older siblings? So the very factor that might increase your risk of say, middle-ear infection decreases your risk of asthma?
Michelle Haby: Yes. The hypothesis is I'm sure you've heard of the hygiene hypothesis is the more older siblings you have, the greater your chance of being exposed to respiratory infections, and there is an hypothesis that they could protect against development of asthma.
Norman Swan: The other risk factors they found were if the child had had hay fever or eczema, a parent with asthma and whether the child had a serious chest infection before the age of two.
But the two things which were most easily changeable and therefore could potentially help prevent asthma were breast feeding and the type of fat intake.
Now there is a theoretical explanation why polyunsaturated fats could make asthma worse. They may fuel inflammation in the immune system. The omega 6 fatty acids in polyunsaturated products are the raw material for a certain kind of inflammatory prostaglandin; I suppose you could call it a biological Wilson Tuckey.
The study wasn't able to say whether fish, with their anti-inflammatory omega 3 fatty acids were protective.
But before you run to the supermarket to turn over your household fats, a couple of words of caution. There were a few problems with the study: for example, the response rate to the questionnaire wasn't as high as the researchers would have liked, which means they may not have selected a typical group of 3-5 year olds.
When it comes to assessing diet, questionnaires are notoriously unreliable.
Michelle Haby: Certainly this finding does not imply causation, it does not imply that polyunsaturated fats cause asthma, nor can we say that if children changed their diet, they can be protected against asthma. What it does say is that here's one more piece of evidence for dietary fat, now let's test them in a well-designed study, preferably a randomised control trial so that we can say whether we can prevent asthma, or actually decrease its severity.
Norman Swan: So the summary then is that the evidence to date is that from these questionnaires that it may well be that a high polyunsaturated diet, say through margarine, using margarine more than you might, may increase the risk of asthma, but it's too early to say whether or not actually eliminating things like margarine from your diet, or replacing it with olive oil margarine is going to make a difference?
Michelle Haby: Exactly, and at this stage we wouldn't be suggesting to children or parents, that the diet should be changed.
Norman Swan: Dr Michelle Haby is in the Centre for Community Child Health at the Royal Children's Hospital in Melbourne.
Haby MM et al. Thorax 2001;56:589-595
- Dr Michelle Haby
- Centre for Community Child Health
Royal Children's Hospital in Melbourne
- Dr Norman Swan