Researchers at Aberdeen University are trying to find out if there's a link between obesity and asthma..
The study into the causes of the condition started in Aberdeen 45 years ago..
Now parents of hundreds of primary school pupils are being urged to take part in the latest stage of the unique survey..
Questionnaires will be sent to several schools..
In 1964 - just 4 per cent of children surveyed in Aberdeen had a history of asthma - in 2004 that figure rocketed to 25 per cent..