Children aged 3 to12 years with diagnosis of asthma were eligible for the study. The clinical criteria for diagnosis of asthma were based on the recommendations of the British Thoracic Society Guidelines, 2009 [14]. The diagnosis of asthma was made if all the following criteria were met: (i) recurrent episodes (³3) of one or more of the following symptoms – wheeze, cough, breathing difficulties and chest tightness, particularly at night or in the early hours of the morning; (ii) respiratory symptoms improve spontaneously or after treatment (bronchodilators with or without corticosteroids); (iii) presence of triggers or aggravating factors such as exposure to allergens or irritants, physical exercise, weather changes or emotional stress; and (iv) personal history of atopy (allergic rhinitis or eczema) and/or family history of atopy (asthma, allergic rhinitis or eczema) in first-degree relatives. The severity of asthma was assessed based on the clinical criteria recommended by the National Heart, Lung, and Blood Institute (NHLBI), and was classified as intermittent asthma or persistent asthma (mild, moderate or severe) [15]. The diagnosis and classification of asthma were performed by three senior pulmonologists who provided specialized care for asthmatic children at the two clinics.

Data collection was carried out through interview with the parents or guardians of the patient using a standard pre-coded questionnaire. All investigators were blinded to the classification of asthma severity. The dependent variable was asthma severity, classified as persistent or intermittent, while independent variables were: dietary habits, demographic and socioeconomic data (gender, age and skin color, family income and educational level of parents), smoking during pregnancy, presence of allergens in the home (curtains, carpets, fluffy toys or pets), gestational age (preterm <37 weeks), birth weight (low birthweight <2500g), family history of asthma (first-degree relatives) and personal history of allergic rhinitis. Dietary habits were determined based on the consumption of specific foods or food groups in the past 12 months. The frequency of food intake was classified into two categories adapted from criteria used in the literature: frequent when intake was three or more times per week, and infrequent when never consumed or intake twice per week or less [12,13]. Specific food or food groups included: milk or yoghurt, meats (bovine, pork, and poultry), vegetables (leafy and non-leafy), fish, eggs, fruit, legumes (beans, peas, lentils, and chick peas), roots and tubers (potato, sweet potato, manioc), grains (rice, pasta, bread), butter, soft drinks and processed foods including fast food. Mediterranean diet pattern (MD) was created based on criteria adapted from the literature: pro-MD pattern (fruit, vegetables, fish, fruit juices, root vegetables and tubers and grains) and a contra-MD diet (milk, meat, eggs, processed foods, soft drinks, butter). The Mediterranean diet was classified as "yes" when intake of at least 5 foods in each group was frequent (³3 times per week) [12]. Nutritional status was measured using the Body Mass Index (BMI) calculated by dividing body mass (Kg) by height2 (m2). The weight was measured by a mechanical platform scale with capacity up to 150 Kg (Filizola) and height was measured by a stadiometer (AlturaExata). Measurements were made using standardized methodology [16]. Nutritional status was classified into two categories according to WHO Reference Growth Standards: Obese, children with a Z-score of BMI-for-age >2 and non-obese, children with a Z-score of BMI-for-age £2 [17].

Statistical analysis: Double data entry was performed using the software EPI-data 3.2. Analyses were carried out using the statistics package Stata 11 (Stata Corp., College Station, USA). A descriptive analysis was conducted for each group with calculation of absolute and relative frequencies for independent variables. Crude and adjusted odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using conditional logistic regression given the matching of cases and controls by age groups [18]. Multivariate analysis was applied to control for potential confounding factors, with inclusion of variables according to the pre-established hierarchical levels as follows: level 1: gender, skin color, maternal schooling, income, paternal schooling, and smoking during pregnancy; level 2: allergens in the home, gestational age, birth weight, family history of allergic rhinitis, exposure to passive smoking; level 3: dietary variables; and level 4: obesity. Only the variables with P £0.20 remained in the model. P<0.05 was considered statistically significant.

TABLE I  Characteristics of the Study Population (N=394) 

TABLE II  Bivariate Analysis of Association Between Dietary Habits and Asthma  Severity  (N=394)

TABLE III Adjusted Analysis of Association Between Patient Characteristics Variables and Asthma Severity

TABLE III Adjusted Analysis of Association Between Patient Characteristics Variables and Asthma Severity

To date, there is limited and inconsistent evidence about association between diet and asthma severity in children. Recently, Ellwood, et al. [4,13] reported the global results of the ISAAC study (Phase III) on the association between food consumption in the last 12 months and atopic diseases such as asthma, rhinoconjuctivitis and eczema. Fruit intake ³3 times per week was found to be a protective factor against severe asthma in both adolescents and children, with OR (95% CI) of 0.89 (0.82-0.97 and 0.86 (0.76-0.97), respectively. Fast food consumption ³3 times per week was a risk factor for severe asthma in two populations, with OR (95% CI) of 1.39 (1.30-1.49) and 1.27 (1.13-1.42), respectively. However, some inconsistent findings were observed between two populations, and there was also heterogeneity of findings across different study centers and countries [13]. In the present study, fruit consumption ³3 times a week appeared to be a protective factor against persistent asthma, with an OR of 0.85 (95% CI 0.48-1.50), although the result was not statistically significant. The conflicting findings regarding the association between Mediterranean diet and asthma severity in children were also found in two studies with similar research methodology and population [11,12]. The inconsistency of the results on diet and asthma severity across different studies, even though among different populations within the same study, may be attributable to sampling error and/or other associated factors such as memory bias, accuracy of the diagnosis and classification of asthma, variation in food types among different geographical regions as well as biological variation among study populations. These factors should be taken into account in the future researches on diet and asthma severity in children.

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