Investigating the association between obesity and asthma among primary schoolchildren in Madinah, Saudi Arabia
Nahhas, Mahmoud A.
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Background: Over the latter half of the last century, a dramatic increase in the prevalence of asthma has been observed. Over this same period there has been a substantial increase in the prevalence of obesity, this giving credence to the hypothesis that obesity and asthma may be causally associated. Aim: The main aims of this thesis were to: i) estimate the prevalence of asthma, allergic rhinitis, and atopic eczema in primary schoolchildren in Madinah, Saudi Arabia; ii) investigate the association between childhood obesity and prevalence of asthma; and iii) investigate possible mechanisms that might explain any associations observed. Methods: I undertook a pilot study aimed at testing the feasibility of conducting a large-scale descriptive epidemiological study of asthma and associated allergic disorders. This was followed by a two-stage cross-sectional survey, which was conducted to investigate the prevalence of asthma, allergic rhinitis, and atopic eczema in a sample of 5,188 schoolchildren, aged 6-8 years using an Arabic, validated version of the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. Finally, I undertook an analytical study investigating the relationship between obesity and asthma. The cross-sectional study allowed for the identification of cases (i.e. those with a history of symptoms suggestive of asthma) and controls (i.e. those without a history suggestive of asthma). A sample of 632 cases and controls were recruited into a matched case-control study. Conditional logistic regression analysis, with appropriate adjustment for a range of potential confounders, was undertaken to explore the association between measures of obesity (in particular, body mass index (BMI)) and asthma. The possible aetiological roles of atopy and airway obstruction were studied by investigating the impact of sensitisation to common aeroallergens and measurements of lung function on the association between body mass index (BMI) and asthma. Results: In the pilot study, I found that the asthma, allergic rhinitis, and atopic eczema were very prevalent in children in Madinah and that further epidemiological studies were therefore likely to be feasible. The overall prevalence of children with a history of symptoms suggestive of asthma was 23.6% (95% CI: 21.3, 26.0); the prevalence among boys was estimated at 24.4% (95% CI: 22.0, 26.9) and among girls at 21.9% (95% CI: 17.4, 27.1), respectively. After adjustment for a number of possible confounders, BMI was found to be a significant predictor of the odds of asthma in both boys (OR=1.11; 95% CI: 1.03, 1.19) and girls (OR=1.38; 95% CI: 1.23, 1.56). When sensitisation to allergens was included in the analyses, the effect of BMI on the risk of asthma was no longer evident in boys (OR=1.09, 95% CI: 0.99-1.19) or girls (OR=1.25; 95% CI: 0.96-1.60). When the effect of lung function measures were factored into the model, the association however persisted: boys: OR=1.10 (95% CI: 1.02, 1.18) and girls OR=1.37 (95% CI: 1.22, 1.54). Conclusions: Asthma and related allergic disorders are very common in primary schoolchildren in Saudi Arabia. BMI is associated with symptoms suggestive of asthma in primary schoolchildren. This effect does not appear to be mediated through respiratory obstruction, but may, at least in part, be mediated through increasing the risk of allergic sensitisation. Prospective and more detailed gender-specific mechanistic studies are now needed to further investigate this association.