Children's teeth will be studied

The top two front teeth begin to develop while babies are in the womb, which means they can tell researchers how well a baby was nourished with trace elements and minerals before birth.

That information may indicate why some children go on to develop wheezing and asthma.

Scientists believe that if a baby does not get enough iron and selenium in the womb, it has an increased risk of developing wheezing in early childhood and possibly asthma later on.

A lot of chronic diseases have their origins before birth, in the womb Dr Seif Shaheen, Kings College London

If the research confirms the link, women could be told to take supplements during pregnancy to prevent their children developing wheezing or asthma.

The amount of selenium people eat has fallen at the same time as asthma rates have been increasing, researchers say.

Selenium occurs naturally in fish, meat, cereals and dairy products, but the richest source is Brazil nuts.

Iron is found in meat, vegetables and cereals.

'Permanent record'

Almost 12,000 milk teeth have been collected as part of the Children of the 90s study, based at the University of Bristol (the Avon Longitudinal Study of Parents and Children - ALSPAC).

Analysis of umbilical cord samples from the ALSPAC study has suggested there could be a connection between the level of exposure to iron and selenium before birth and subsequent risk of wheezing.

But it is only with the collection of the milk teeth that researches can accurately check children's exposure to the minerals.

Researchers will now analyse the milk teeth of 250 children with asthma and 250 children without asthma.

Dr Seif Shaheen, from Kings College London, who will help carry out the study, said: "Milk teeth begin to develop before birth and the enamel takes up trace elements and minerals, thus capturing a permanent record of exposure.

"When milk teeth drop out the enamel can be analysed to look back in time and tell us about a baby's actual level of exposure to trace elements and minerals before birth."

He added: "A lot of chronic diseases have their origins before birth, in the womb.

'Excited'

"Clues are emerging to suggest that factors which influence the development of the lung and immune system of a baby in the womb are likely to play an important part in determining whether they subsequently suffer from wheezing and asthma as children.

"We have preliminary evidence to suggest that babies exposed to higher levels of selenium in utero have a lower risk of persistent wheezing in early childhood, and those exposed to higher levels of iron have a lower risk of later onset wheezing and eczema."

Philippa Major, assistant director of research for the National Asthma Campaign, which is funding the research, said: "Asthma is the most common long term condition in the UK today.

"One of our most urgent research priorities is to address the primary prevention of asthma in children.

"We are excited and pleased to be funding this ground-breaking research which will help us to identify what causes asthma to develop in children."