Incidence and burden of allergic conditions and the effects of birthweight and growth on wheezing disorders in the Born in Bradford cohort

Past epidemiologic studies have claimed that birthweight, body mass index, and childhood growth are associated with childhood wheezing disorders although the findings are inconsistent. The aim of this thesis was to investigate the effects of birthweight body mass index and childhood growth on wheezing disorders through meta-analyses of past epidemiologic studies and using contemporary cohort data. An online search of published papers linking childhood wheezing disorders with birthweight, BMI, and growth was carried out using EMBASE and Medline medical research databases. Risk estimates were pooled using a random-effects method. Data from 13,734 Born in Bradford (BiB) cohort children were used to investigate the incidence and burden of allergic diseases, and the effects of birthweight on wheezing disorders. Data of 1,598 BiB1000 children were used to investigate the effects of weight at the age of 3 years and childhood growth on wheezing disorders. Birthweight was categorised using the World Health Organisation and Centre for Disease Prevention and Control guidelines. Weight Standardised Scores were derived using World Health Organisation growth standards. Body mass index was categorised based on Centre for Disease Prevention and Control guideline. Based on a total of 77 studies that comprised more than 3 million children, the summary risk estimates indicated that low birthweight children have an increased risk of wheezing disorders when compared with the normal birthweight children. In addition, underweight children have a reduced risk of wheezing disorders whilst overweight and obese children have an increased risk when compared with normal body mass index children. Based on the cohort data, the results indicate that the burden of allergic conditions is higher than previously reported in earlier studies. In addition, there is an increased risk of wheezing disorders for low birthweight, slow growth during the first three months, and fast growth between 3 and 12 months.