Previous studies have suggested expanding waistlines could boost childhood asthma cases.
But scientists at Bristol University have now linked obesity to an increased risk of the respiratory disease.
A study found the relative risk of asthma increased by 55 per cent for every extra unit of body mass index (BMI).
The incidence of asthma – a chronic condition caused by inflammation of the airways – has been rising steadily over the past few decades, with more than 1.1 million children in the UK currently battling the disease.
Leading charity Asthma UK today welcomed the study.
Dr Samantha Walker, the charity’s director of research and policy said: ‘This research shows that children with a high BMI are more likely to develop asthma and is in line with previous research linking obesity with asthma.
‘Asthma in children is a complex condition, and more research is needed to find ways to prevent asthma attacks and tragic asthma deaths.
‘Keeping your BMI within normal limits brings all sorts of health benefits and may help reduce the risk of children developing asthma.’
Latest figures show 18.9 per cent of children in Year 6 aged 10 to 11 were obese and a further 14.4 per cent were overweight.
Of the children in Reception aged four to five, latest figures suggest 9.3 per cent were obese and another 13.0 per cent were overweight.
In total almost a third of 10 to 11-year-olds and more than a fifth of four to five-year-olds were overweight or obese.
Although the underlying causes of asthma are not known some experts think obesity may be one of the causes.
Previous research had suggested a link between obesity and asthma but the new study published in PLOS Medicine used both genetic information and observational data in order to assess whether BMI has a causal effect on asthma.
The study looked at 4,835 children with asthma by the age of seven-and-a-half enrolled in the Avon Longitudinal Study of Parents and Children.
A weighted genetic score based on 32 independent BMI-related DNA sequence variations was calculated, and associations with BMI, fat mass, lean mass, and asthma were estimated.
The research found that the genetic score was strongly associated with BMI, fat mass, and lean mass, and with childhood asthma, and that the relative risk of asthma increased by 55 per cent for every extra unit of BMI.
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.
There was also some evidence that body composition – lean body mass – influences asthma through pathways not related to obesity-induced inflammation.
Dr Raquel Granell said: ‘Environmental influences on the development of asthma in childhood have been extensively investigated in epidemiological studies, but few of these provide strong evidence for causality.
‘Higher BMI in mid-childhood could help explain some of the increase in asthma risk toward the end of the 20th century, although the continued rise in obesity but with a slowing in the rise in asthma prevalence in some countries implies that other non-BMI-related factors are also likely to be important.’