VITAMIN D RELATED BEHAVIOURS AMONG PREGNANT WOMEN IN AUSTRALIA Yue Wu Paediatrician, MMed, BM Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy School of Public Health & Social Work Faculty of Health Institute of Health and Biomedical Innovation Queensland University of Technology October 2013 Keywords Vitamin D, pregnant women, sun exposure, sun protection, dietary intake, supplement, pregnancy outcomes Vitamin D Related Behaviours Among Pregnant Women in Australia i Abstract Maternal vitamin D deficiency during pregnancy has numerous health implications in both the mothers and their offspring, therefore, it is important to prevent women from vitamin D deficiency during this period. Even in Australia, with high levels of sunlight (which is the primary source of vitamin D in human beings), pregnant women have been reported to be at increased risk of vitamin D deficiency. Because the determinants of vitamin D status are skin exposure to sunlight and oral intake of vitamin D from both foods and supplements, an individual’s vitamin D status is affected by his or her sun exposure behaviours, such as time spent outdoors, clothing coverage and sunscreen use, as well as dietary behaviours. However, there is a lack of basic observational data on those sun exposure and dietary behaviours in pregnant women. In consideration of the high prevalence of vitamin D deficiency in pregnant women, and making effective strategies to prevent this issue, it is important to understand how pregnant women behave in regard to sun exposure and vitamin D intake. This study aims to investigate these vitamin D related behaviours, including time outdoors, clothing, sunscreen use, dietary vitamin D intake and vitamin D supplement ingestion among pregnant women in Australia. One hundred and sixty- four pregnant women throughout Australia participated in web-based questionnaires with regard to their vitamin D related behaviours and the potential influencing factors, such as demographics, obstetrical variables, their knowledge and attitudes to vitamin D. Subsequently, 132 out of the whole 164 women completed a follow-up, online, pilot survey after their delivery to report their pregnancy outcomes, which aimed to explore the potential link between maternal vitamin D related behaviours during pregnancy and pregnancy outcomes. The mean outdoor time for pregnant women in Australia was 52.46 (95% CI: 45.60 – 60.34) minutes per day(median: 60 minutes per day) on weekdays and was 89.12 (95% CI: 77.48 – 102.51) minutes per day (median: 90 minutes per day) on weekends. On average, 78% of their skin was covered by clothing whilst outdoors. Approximately half of the women applied sunscreen in the previous month. ii Vitamin D Related Behaviours Among Pregnant Women in Australia The median dietary intake among these pregnant women was only 1.38 μg per day from foods. Of those who responded, 22.6% did not use of vitamin D supplements, whereas 12.8% reported consuming < 500 IU per day. Women living in a low ambient temperature or ultraviolet radiation environment covered their skin more with clothing, but were less likely to apply sunscreen. Women on ≥ 500 IU per day vitamin D supplements covered their skin more with clothing and tended to have less UV adjusted, outdoor time. No significant differences were found between maternal vitamin D related behaviours and pregnancy outcomes in the follow-up, pilot study. In conclusion, pregnant women in Australia have low sun exposure and limited vitamin D intake, which may explain why pregnant women are prone to vitamin D deficiency in this country. Main findings: Pregnant women in Australia get limited sun exposure. The intake of vitamin D from foods is low in Australian pregnant women who participated in this study. The application of vitamin-D-containing supplements in Australian pregnant women is greater than other populations in both proportion and amount, but for the majority of them, the intake amount still does not meet the current recommendations (15 μg per day). Vitamin D Related Behaviours Among Pregnant Women in Australia iii Table of Contents KEYWORDS ....................................................................................................................................... I ABSTRACT ...................................................................................................................................... II TABLE OF CONTENTS ................................................................................................................... IV LIST OF TABLES ............................................................................................................................ VII LIST OF FIGURES ........................................................................................................................... IX LIST OF ABBREVIATIONS .............................................................................................................. X STATEMENT OF ORIGINAL AUTHORSHIP ............................................................................. XI ACKNOWLEDGEMENTS .............................................................................................................. XII CHAPTER 1: INTRODUCTION ....................................................................................................... 1 1.1 BACKGROUND AND RATIONALE FOR THE STUDY ..................................................... 1 1.1.1 Background ................................................................................................................. 1 1.1.2 Rationale for this Study .............................................................................................. 8 1.2 RESEARCH AIM, OBJECTIVES AND RESEARCH QUESTIONS ..................................... 8 1.3 SIGNIFICANCE ....................................................................................................................... 9 1.4 THESIS OUTLINE ................................................................................................................. 10 CHAPTER 2: LITERATURE REVIEW ......................................................................................... 11 2.1 INTRODUCTION .................................................................................................................. 11 2.2 BACKGROUND OF VITAMIN D ........................................................................................ 12 2.2.1 Sources of Vitamin D................................................................................................ 12 2.2.2 Metabolism of Vitamin D ......................................................................................... 13 2.2.3 Assessment of Vitamin D Status ............................................................................... 14 2.2.4 Classification of Vitamin D Status ............................................................................ 15 2.2.5 Function of Vitamin D .............................................................................................. 16 2.2.6 Epidemiology of Vitamin D Deficiency ................................................................... 19 2.2.7 Causes of Vitamin D Deficiency .............................................................................. 19 2.2.8 Prevention and Treatment for Vitamin D Deficiency ............................................... 21 2.2.9 Vitamin D in Australia .............................................................................................. 23 2.3 VITAMIN D IN PREGNANCY ............................................................................................. 24 2.3.1 Adaptations of Vitamin D Metabolism in Pregnancy ............................................... 25 2.3.2 Prevalence of Vitamin D Deficiency in Pregnancy ................................................... 26 2.3.3 Maternal Health Consequences of Vitamin D Deficiency in Pregnancy .................. 27 2.3.4 Offspring Health Consequences of Maternal Vitamin D Deficiency in Pregnancy ................................................................................................................. 29 2.4 STUDIES OFBEHAVIOURS IN RELATION TO VITAMIN D .......................................... 33 2.5 SUMMARY ............................................................................................................................ 35 CHAPTER 3: RESEARCH DESIGN ............................................................................................... 37 3.1 RESEARCH DESIGN ............................................................................................................ 37 3.2 SAMPLE ................................................................................................................................. 38 3.2.1 Inclusion Criteria ...................................................................................................... 38 3.2.2 Sample Size Calculation ........................................................................................... 38 3.3 QUESTIONNAIRE DEVELOPMENT .................................................................................. 39 3.3.1 The Baseline Survey ................................................................................................. 40 3.3.2 The Follow-up Survey .............................................................................................. 41 iv Vitamin D Related Behaviours Among Pregnant Women in Australia 3.4 SURVEY TEST AND ACTIVATION ..................................................................................