Researchers have found the chances of developing asthma increases as a child's weight goes up.
Scientists from the University of Queensland Diamantina Institute and the UK's Bristol University found the relative risk of asthma increased by 55 per cent for every extra unit of body mass index (BMI).
Asthma prevalence in Australia is high by international standards - one in 10 people in Australia has asthma.
And doctors have known for years that there's an observational relationship between how overweight a person is and their risk of asthma.
But this is the first time researchers have been able to demonstrate a causal link between the two.
Professor David Evans from the University of Queensland Diamantina Institute said the researchers employed a new method that uses both genetic information and observational data in order to assess whether BMI has a causal effect on asthma.
They investigated the link in 5000 children aged seven-and-a-half years.
"Basically the idea is if you take genes that you know are related to being overweight - and if being overweight causes asthma - then you'd expect that those genes would be related to increased risk of asthma.
"This is exactly what we found."
These findings suggest that a higher BMI increases the risk of asthma in mid-childhood, and that public health interventions designed to reduce obesity may also help to limit the global rise in asthma.
The incidence of asthma - a chronic condition caused by inflammation of the airways - has been rising steadily over the past few decades.
It is estimated that up to 300 million adults and children worldwide are affected by asthma.
Although asthma can develop at any age, it is often diagnosed in childhood.