Fruits, vegetables and the Mediterranean diet could reduce the risk of asthma and allergies in children

Diet has been recently recognized as a potential risk factor for asthma and allergic disorders, although the epidemiological evidence to date is still conflicting. We recently found a beneficial effect of commonly consumed fruits, vegetables and nuts, and of a high adherence to a traditional Mediterranean diet during childhood on symptoms of asthma and rhinitis.

The survey was conducted in 2001, in four rural areas of the Mediterranean island of Crete in Greece. School children aged between 7 and 18 years were invited to participate in the study (n=690). The parents were invited to complete a questionnaire that included questions on the child’s respiratory and allergic symptoms, family history of allergic diseases, birth order and sibling numbers, levels of parental education and occupation. A detailed food frequency questionnaire of 58 items was used to assess usual dietary intake in children. The degree of adherence to a traditional Mediterranean diet was based on the KidMed index, a Mediterranean Diet quality index constructed to evaluate food habits in a population of Spanish children. The index ranged from 0 to 10, and was categorised into three levels: ⁽¹⁾ ≥6, optimal Mediterranean diet; ⁽²⁾ 4–5, medium quality Mediterranean diet; ⁽³⁾ ≤3, low quality Mediterranean diet. The prevalence of any wheezing, and rhinitis symptoms in the past were 16.8% and 18.7% respectively. When these symptoms were combined with atopy, the prevalence rates for wheezing and rhinitis were 5.4% and 6.7% respectively.

At least twice a day, 80% of children ate fresh fruit, and 68% ate vegetables. Daily consumption of grapes, oranges, apples, and fresh tomatoes was found to have beneficial effect on wheezing symptoms. Daily intake of grapes was also inversely associated with current allergic rhinitis and current seasonal allergic rhinitis after adjusting for potential confounders. Consumption of nuts more than three times per week was inversely associated with wheezing, whereas weekly intake of margarine appeared to be harmful on asthma and allergic rhinitis symptoms. There were 27.9% of children who had a low quality of Mediterranean Diet according to KidMed index, 43.8% who had intermediate values, and 28.3% with a high index. A high level of adherence to the Mediterranean diet was found to be protective for allergic rhinitis, while a more modest protection was observed for wheezing and atopy.

The prevalence of asthma and allergic diseases has increased dramatically over the past few decades with the highest incidence occurring in children. Epidemiological and immunological studies suggest that dietary modification or supplementation in childhood could reduce the development of allergic disorders. Fruits and vegetables are rich sources of antioxidant vitamins such as vitamins C, E and carotenoids, and other antioxidants such as selenium and flavonoids, that are thought to reduce airway inflammation by protecting airway cells from endogenous and exogenous oxidative damage. Nuts are a very rich source of vitamin E, the body’s principal defence against oxidant-induced membrane injury in human tissue, via its role in breaking the lipid peroxidation chain reaction. On the other hand, margarine is a rich source of omega-6 polyunsaturated fatty acids (PUFAs) that promote the formation of prostaglandins with a consequent increase in the likelihood of atopic sensitization, asthma, and atopic disease.

Dietary patterns such as the Mediterranean Diet account for cumulative and interactive effects among nutrients, reflect real-world-dietary preferences, and may be particularly suitable for analysis in asthma epidemiology where many dietary components could be related with the outcome of interest. The results of the present study, indicating a protective effect of children’s adherence to the Mediterranean diet on rhinitis and asthma symptoms probably reflect a high exposure to several antioxidant compounds and their adverse effect on the oxidative stress damage of lung tissues.