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Thursday, 19 July, 2001, 00:25 GMT 01:25 UK
Margarine 'may increase asthma risk'
Margarine
Margarine consumption has risen in recent years
A diet high in polyunsaturated fats - found in many margarines and vegetable oils - may double a child's chances of having asthma, according to researchers.

The link emerged from a comprehensive study of asthma risk factors in pre-school children aged between three and five in Australia.

The study also found that being breastfed as a baby and having three or more older siblings seemed to protect against the development of asthma.

Inhaler
Asthma is on the increase
The children were from two rural cities in Australia, one with a humid climate close to the coast and the other with a dry inland climate.

They were chosen because the children who lived there were exposed to different types of allergy-causing substances.

Parents of almost 1000 children completed a questionnaire, which included questions on asthma diagnosis, symptoms, and medicine in the preceding 12 months for their children, number of children in the family, whether the child was breastfed, and consumption of dietary polyunsaturated fats.

Skin prick test

Some 650 of these children also took a skin prick test to assess their response to common allergens including dust mite, egg, cow's milk, and rye grass.

Around one in five children had asthma. A child with an allergic response to one or more components of the skin prick test was almost 2.5 times as likely to have recent asthma as children with a negative test.


We are still a long way from being able to explain why this common disease is becoming more common

Dr Martyn Partridge
A parent with asthma doubled the risk and a serious respiratory infection before the age of two increased the risk by 93 per cent.

But one of the strongest links was to a diet high in polyunsaturated fat.

This was defined as a diet which included margarine spread on bread, and foods regularly fried in polyunsaturated vegetable oils.

Children who ate this type of diet were at a more than doubled risk of developing asthma. The researchers believe that it could account for up to 17% of cases of childhood asthma.

Explanation

Lead researcher Dr Michelle Haby, from the Centre for Community Child Health, Royal Children's Hospital, Melbourne, told BBC News Online why polyunsaturated fats might be linked to asthma.

"Polyunsaturated fats are a rich source of omega-6 fatty acids, such as linoleic acid, which can increase the synthesis of a substance called prostaglandin E2.

"The net effect is to increase the risk of inflammation, which may increase the risk of asthma.

"Omega-3 fatty acids have the opposite effect by inhibiting the formation of prostaglandin E2 and protecting against inflammation.

"Thus, reduced consumption of omega-3 fatty acids may also increase the risk of asthma due to a loss of protection against inflammation."

The authors suggest that the increase in the number of children developing asthma could be significantly reduced if more were breastfed or given a diet lower in polyunsaturated fats.

However, Dr Haby said more research was needed before the link between polyunsaturated fats and asthma could be proved.

Dr Martyn Partridge, National Asthma Campaign's chief medical adviser said: "The new evidence in this paper that suggests a reduction in consumption of dietary polyunsaturated fats may also reduce the likelihood of developing asthma is helpful, but we are still a long way from being able to explain why this common disease is becoming more common."

Dr Warren Lenney, a spokesperson for the British Thoracic Society (BTS), said: "It would be sensible for parents to lessen their children's intake of margarine and foods regularly fried in polyunsaturated oil as part of a diet rich in fruit and vegetables."

The research is published in the journal Thorax.

See also:

07 Jun 01 | Health
Bacteria 'cause asthma'
17 May 01 | Health
Damp homes 'increase asthma risk'
03 May 01 | Health
Simple treatment for asthma
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