Prenatal vitamin D for the prevention of preschool wheezing Effect on early lung development Dr Stephen Goldring Imperial College London Department of Paediatrics Thesis to be submitted for MD (Res) May 2014 1 Declaration of originality All the work in this thesis is my own except where referenced. Copyright declaration The copyright of this thesis rests with the author and is made available under a Creative Commons Attribution Non-Commercial No Derivatives License. Researchers are free to copy, distribute or transmit the thesis on the condition that they attribute it, that they do not use it for commercial purposes and that they do not alter, transform or build upon it. For any reuse or redistribution, researchers must make clear to others the license terms of this work. 2 Abstract Background: Asthma is the commonest chronic disease of childhood. The earliest manifestation is often preschool wheezing, which affects up to 50% of young children, but is difficult to evaluate practically. Observational studies suggest that low prenatal vitamin D status may be a risk factor for childhood wheezing. Aims: To evaluate the measurement of preschool lung function using impulse oscillometry, and to test the hypotheses that prenatal vitamin D supplementation may promote lung development or prevent preschool wheezing. Methods: We recruited 3 to 5 year olds from outpatient clinics to evaluate the quality of impulse oscillometry readings and the relationship between lung function and wheezing. We then evaluated impulse oscillometry in a group of 3-year-old children whose mothers had participated in a prenatal vitamin D supplementation trial. Next we evaluated the effect of prenatal vitamin D supplementation on lung function parameters and on the prevalence of wheeze and atopy in the first 3 years of life in this population (ISRCTN 68645785). Findings: In 3 to 5 year old children, we successfully acquired high quality impulse oscillometry readings in 37/66 (56%). We found increased bronchodilator responses in those who had previously wheezed, with adjusted mean difference in respiratory resistance at 25Hz (95% confidence intervals) of -8.65 Kpa/Ls-1 (-16.63, -0.67), p=0.04. In 3-year-old children whose mothers participated in a prenatal vitamin D trial, we acquired high quality readings in 51/105 (49%), but found no relationship between wheezing history and bronchodilator response. In the randomised controlled trial of prenatal vitamin D supplementation, we evaluated 158/180 (88%) offspring at age 3 years and found no difference in wheeze, atopy, lung function or healthcare utilisation between vitamin D supplemented groups and controls. Conclusions: It is possible to acquire high quality lung function data using impulse oscillometry for half of preschool children, however we found no consistent relationship 3 between lung function and wheezing history. There may be age related differences in the pathophysiology of wheezing and its relationship to lung function, which should be explored in future studies. Prenatal vitamin D supplementation in late pregnancy was not associated with differences in lung function or wheezing. Future research should explore the effect of higher doses and earlier administration of vitamin D in pregnancy. 4 Table of contents Abstract 3 Table of contents 5 List of Tables 8 List of Figures 11 Acknowledgments 12 Publications 13 1 Literature review 14 1.1 Abstract 14 1.2 Asthma and preschool wheezing 15 1.3 Pathophysiology of asthma 21 1.4 Lung function assessment in preschool children 24 1.5 Early life origins of asthma 34 1.6 Nutritional interventions for Primary Prevention of asthma 48 1.7 Vitamin D physiology 50 1.8 Evidence of an association between prenatal vitamin D status and child health 60 1.9 Potential mechanisms: Vitamin D and early lung development 75 1.10 Potential mechanisms: Vitamin D and immune development 81 1.11 Public health importance 89 1.12 Conclusions 91 1.13 Aims of the thesis 91 2 General Methods 92 2.1 Pilot study to evaluate the feasibility of impulse oscillometry in preschool children 92 5 2.2 Follow up study of a randomised controlled trial of prenatal vitamin D supplementation to evaluate its effect on respiratory and allergic outcomes in childhood. 95 2.3 An evaluation of the effects of prenatal vitamin D supplementation on healthcare utilization in the first three years of life 104 3 Assessment of lung function in 3 to 5 year old children attending a paediatric outpatient department using impulse oscillometry 110 3.1 Introduction 110 3.2 Methods 111 3.3 Results 111 3.4 Discussion 138 4 Effect of prenatal vitamin D supplementation on parentally reported outcomes 142 4.1 Introduction 142 4.2 Methods 143 4.3 Results 143 4.4 Discussion 168 5 Effect of prenatal vitamin D on atopy, inflammation and lung function 172 5.1 Introduction 172 5.2 Methods 173 5.3 Results 173 5.4 Discussion 191 6 Effect of prenatal vitamin D on healthcare utilisation in offspring 192 6.1 Introduction 192 6.2 Methods 193 6.3 Results 193 6.4 Discussion 208 6 7 Assessment of lung function in 3 year old children whose mothers participated in a vitamin D supplementation trial during pregnancy using impulse oscillometry 210 7.1 Introduction 210 7.2 Methods 210 7.3 Results 210 7.4 Discussion 226 8 Discussion 228 8.1 Assessment of lung function in preschool children using impulse oscillometry 228 8.2 Effect of prenatal vitamin D on child health 230 9 References 232 10 Appendices 278 10.1 Pilot study participant information sheet 278 10.2 Pilot study consent form 282 10.3 Pilot study – general health questionnaire 283 10.4 Pilot study – wheezing questionnaire 287 10.5 Main study - participant information leaflet 296 10.6 Main study - consent form 300 10.7 Main study questionnaire 301 7 List of Tables Table 9.1 Associations between phenotypes and clinical outcomes in the ALSPAC study. ................. 17 Table 9.2 Studies investigating the ability of IOS to discriminate between preschool children with and without wheeze or asthma. ....................................................................................................................... 31 Table 9.3 Nutrients and foods for the primary prevention of asthma ........................................................ 45 Table 9.4 Vitamin D status of pregnant women and their offspring in cross sectional studies worldwide ................................................................................................................................................................ 56 Table 9.5 Epidemiological associations between early life vitamin D status and allergic or respiratory health ................................................................................................................................................. 63 Table 10.1 Diagnostic codes for electronic health records........................................................................... 105 Table 11.1 Children with and without a history of wheezing ...................................................................... 113 Table 11.2 Baseline IOS parameters (pilot study) with age in months .................................................... 116 Table 11.3 Baseline IOS parameters (pilot study) in boys vs girls ............................................................ 118 Table 11.4 Coefficient of variation for impulse oscillometry measurements ....................................... 122 Table 11.5 Coefficient of variation for impulse oscillometry in children with and without wheezing ................................................................................................................................................................................... 123 Table 11.6 Baseline lung function in preschool children with and without a history of wheeze ... 126 Table 11.7 Baseline lung function in preschool children with and without atopic skin sensitisation ................................................................................................................................................................................... 127 Table 11.8 Baseline lung function in preschool children with and without atopic wheeze ............. 128 Table 11.9 Baseline lung function in preschool children with and without any ETS exposure ...... 129 Table 11.10 Baseline lung function in preschool children with and without frequent URTI .......... 130 Table 11.11 Bronchodilator response in children with and without a history of wheezing ............ 133 Table 11.12 Bronchodilator response in children with and without a history of atopy ................... 134 Table 11.13 Bronchodilator response in children with and without a history of atopic wheezing ................................................................................................................................................................................... 135 Table 11.14 Bronchodilator response in children with and without a history of any ETS exposure ................................................................................................................................................................................... 136 8 Table 11.15 Bronchodilator response in children with and without a history of frequent URTI .. 137 Table 11.16 Bronchodilator responses for asthmatic/wheezy children vs controls .......................... 140 Table 12.1 Study participants .................................................................................................................................. 146 Table 12.2 Parentally