Early-Life and Childhood Factors’ Association with Diabetes: Caesarean Section, Birth Order and Daycare Attendance on Type 1 Diabetes Risk, and Childhood Developmental Conditions and Education on Early-onset Adult Diabetes Risk

Abstract

Using comprehensive data from two large population-based studies consisting participants with a wide age-range and online literature databases, this dissertation investigated the influence of Caesarean section birth, birth order, daycare attendance and sex on the risk of childhood- and adult-onset type 1 diabetes, as well as early-onset adult diabetes (diagnosed at age 20 – 40 years). The results showed no association between birth by Caesarean section and type 1 diabetes risk after accounting for relevant confounding factors, particularly parental diabetes history and migration background. However, summarized risk estimates from published studies in a meta-analysis demonstrated a slightly increased type 1 diabetes risk in children and young adults associated with elective Caesarean birth following adjustment of various potential confounding factors. Furthermore, reduced childhood- and adult-onset type 1 diabetes risk was consistently observed among higher-order born individuals in the last few decades. These results support the hypotheses that the presence of labour is beneficial to the immune system development of the infant, and that early-life exposure to a rich variety of microbiome could assist optimal gut microbiome maturation, whose alterations might have repercussions beyond childhood. A lower adult-onset type 1 diabetes risk among females was also seen in another study, providing further evidence that around or after puberty sex differences played a role in type 1 diabetes manifestation. The results also demonstrated the disadvantageous roles of urban living in childhood and high education towards early-onset adult diabetes in a developing country. The association were likely due to the facilitation of exposure and establishment of imbalanced diet and sedentary lifestyle from a very young age, thereby contributing to increased type 2 diabetes risk in later-life. Hence, this dissertation added to existing literature that (i) taking into account both parents’ diabetes history reduced the association between Caesarean section birth in general and type 1 diabetes risk, (ii) elective Caesarean section birth, which bypasses the labour process, was related to higher type 1 diabetes risk in children and young adults, (iii) birth order and sex should be taken into account in adult-onset type 1 diabetes risk assessment for early diagnosis, (iv) child health programs in urban areas of developing countries should promote diabetes awareness for early prevention.