Teenagers and young children who eat fast food could be increasing their risk of developing asthma, eczema and hay fever, according to a study published Monday in the British Medical Journal's respiratory journal Thorax.

The International Study of Asthma and Allergies in Childhood (ISAAC) study used written questionnaires completed by 319,196 13- and 14-year-olds from 51 countries and by the parents of 181,631 6- and 7-year-olds in 31 countries. They were asked if they had symptoms of the three conditions and about their weekly diet – including the types of foods they ate over the last year, and how often.

"We found clear associations between certain foods and severe asthma, hay fever (or allergic rhinoconjunctivitis) and eczema in the largest study of allergies in children (aged 6-7 years) and adolescents (13-14 years) to date," said study author Hywel Williams of the Centre for Evidence Based Dermatology, Queen's Medical Centre, University Hospital, Nottingham, UK. According to Williams, the associations between allergic diseases and fast food were "only really convincing for severe disease."

Researchers saw a protective effect against severe asthma for those who ate fruit at least three times a week. Those consuming fast food three or more times a week had about a 30% increased risk of severe asthma, hay fever and eczema, a chronic skin condition that causes scaly, itchy rashes. The results were consistent in both age groups. Affluence and gender did not change or affect the outcome.

Read - Asthma, eczema and hay fever may be linked to fast food