The data, from more than 500,000 children in over 50 countries suggests that poor dietary habits may be the cause of increasing levels of allergy-related conditions such as asthma and eczema in children and adolescents.
Writing in the BMJ’s Thorax journal, the international team of researchers reveal that young teenagers in particular are nearly 40% more likely to have severe asthma if they consume common junk foods that are high in levels of sugars and fats more than three times a week.
For children aged six to seven the risk increased by 27%, said the researchers led by Professor Innes Asher, from the University of Auckland in New Zealand, and Prof Hywel Williams, from the University of Nottingham in the UK.
"If the associations between fast foods and the symptom prevalence of asthma, rhinoconjunctivitis and eczema is causal, then the findings have major public health significance owing to the rising consumption of fast foods globally," they said.
Junk food consumption was also found to be linked with severe eczema and rhinitis, said Asher and his colleagues.
However, the team added that eating fruit appeared to offer protection for young people – with those consuming more than three portions a week reducing the severity of their symptoms by 11% among teenagers and 14% among younger children.
The study findings are as the result of a large collaborative project called the International Study of Asthma and Allergies in Childhood (ISAAC), which involves nearly 2 million children in more than 100 countries, making it the biggest of its kind.
The ‘fast food study’ reported here involved a small proportion of the children taking part in ISAAC, from two age groups: 319,000 13- to 14-year-olds from 51 countries and 181,000 six- to seven-year-olds from 31 countries.
As part of this smaller study, children and their parents were sent questionnaires to measure eating habits over the previous 12 months. They were asked how often they had eaten specific foods, including meat, fish, fruit and vegetables, pulses, cereals, bread and pasta, rice, butter, margarine, nuts, potatoes, milk, eggs, and fast food/burgers.
They were also asked whether and how often they suffered from specific asthma and allergy symptoms – and if so, how severe they were and whether they stopped them sleeping or interfered with daily life.
Fast food and ‘burgers’ were the only food type associated with asthma and allergies across all age ranges and countries, they revealed.
Asher and his team suggested that "such consistency adds some weight to the possible causality of the relationship."
However they said more research is now needed in order to discover whether junk food and fast food is a cause of such conditions.
Published online ahead of print, doi: 10.1136/thoraxjnl-2012-202285
“Do fast foods cause asthma, rhinoconjunctivitis and eczema? Global findings from the International Study of Asthma and Allergies in Childhood (ISAAC) Phase Three”
Authors: Philippa Ellwood, M Innes Asher, Luis García-Marcos, Hywel Williams, Ulrich Keil, Colin Robertson, Gabriele Nagel, the ISAAC Phase III Study Group