Joachim Rosenbauer, G. Devoti, Geir Joner, Emma Jane Kirsty Wadsworth, Lee-Ming Chuang, Edith Schober, Girts Brigis, Constantin Ionescu-Tirgoviste, Christopher Glatthaar, Katja Radon, Johnny Ludvigsson, B. Urbonaite, Thomas Waldhoer, Sandra Sipetic, Carine de Beaufort, Christopher Patterson, Karsten Buschard, Przemysława Jarosz-Chobot, Ondrej Cinek, Max Bulsara, Michael J Goldacre, Christine L. Roberts, Amanda G. Chetwynd, Denka Stoyanov, Roger C Parslow, Jannet Svensson, Christopher Cardwell, Suely Godoy Agostinho Gimeno, Lars C. Stene, Queens Univ Belfast, Norwegian Inst Publ Hlth, Oslo Univ Hosp, Univ Oslo, Univ Western Australia, Univ Notre Dame, Charles Univ Prague, Univ Dusseldorf, Linkoping Univ, Glostrup Univ Hosp, Univ Oxford, Med Univ Vienna, Med Univ Silesia, Universidade Federal de São Paulo (UNIFESP), Natl Taiwan Univ Hosp, Univ Sydney, Univ Leeds, Cardiff Univ, Univ Lancaster, Riga Stradins Univ, Kaunas Univ Med, Univ Belgrade, Univ Lecce, N Paulescu Inst Diabet, Pediat Clin, Childrens Diabet Ctr, Rigshosp, Hosp LMU Munich, Sir Charles Gairdner Hosp, Cardwell, Cr, Stene, Lc, Joner, G, Bulsara, Mk, Cinek, O, Rosenbauer, J, Ludvigsson, J, Svensson, J, Goldacre, Mj, Waldhoer, T, Jarosz Chobot, P, Gimeno, Sg, Chuang, Lm, Roberts, Cl, Parslow, Rc, Wadsworth, Ej, Chetwynd, A, Brigis, G, Urbonaité, B, Sipetic, S, Schober, E, Devoti, Gabriele, Ionescu Tirgoviste, C, de Beaufort, Ce, Stoyanov, D, Buschard, K, Radon, K, Glatthaar, C, and Patterson, C. C.
Czech Republic Ministry of Education Department of Health of Taiwan Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Swedish Child Diabetes Foundation NHS National Coordinating Centre for Research Capacity Development UK Australian National Health and Medical Research Council (NHMRC) Research Council of Norway German Research Foundation Ministry for Science and Technological Development of Serbia European Commission Health Information Strand Diabetes UK Northern Ireland Department of Health and Social Services Background the incidence rates of childhood onset type 1 diabetes are almost universally increasing across the globe but the aetiology of the disease remains largely unknown. We investigated whether birth order is associated with the risk of childhood diabetes by performing a pooled analysis of previous studies.Methods Relevant studies published before January 2010 were identified from MEDLINE, Web of Science and EMBASE. Authors of studies provided individual patient data or conducted pre-specified analyses. Meta-analysis techniques were used to derive combined odds ratios (ORs), before and after adjustment for confounders, and investigate heterogeneity.Results Data were available for 6 cohort and 25 case-control studies, including 11 955 cases of type 1 diabetes. Overall, there was no evidence of an association prior to adjustment for confounders. After adjustment for maternal age at birth and other confounders, a reduction in the risk of diabetes in second- or later born children became apparent [fully adjusted OR = 0.90 95% confidence interval (CI) 0.83-0.98; P = 0.02] but this association varied markedly between studies (I(2) = 67%). An a priori subgroup analysis showed that the association was stronger and more consistent in children < 5 years of age (n = 25 studies, maternal age adjusted OR = 0.84 95% CI 0.75, 0.93; I(2) = 23%).Conclusion Although the association varied between studies, there was some evidence of a lower risk of childhood onset type 1 diabetes with increasing birth order, particularly in children aged < 5 years. This finding could reflect increased exposure to infections in early life in later born children. Queens Univ Belfast, Ctr Publ Hlth, Sch Med Dent & Biomed Sci, Belfast BT12 6BJ, Antrim, North Ireland Norwegian Inst Publ Hlth, Div Epidemiol, Oslo, Norway Oslo Univ Hosp, Oslo Diabet Res Ctr, Oslo, Norway Univ Oslo, Inst Hlth Management & Hlth Econ, Oslo, Norway Univ Western Australia, Telethon Inst Child Hlth Res, Ctr Child Hlth Res, Perth, WA 6009, Australia Univ Notre Dame, Inst Hlth & Rehabil Res, Fremantle, Australia Charles Univ Prague, Sch Med 2, Prague, Czech Republic Univ Dusseldorf, Leibniz Inst, Inst Biometr & Epidemiol, German Diabet Ctr, Dusseldorf, Germany Linkoping Univ, Dept Paediat, Linkoping, Sweden Linkoping Univ, Diabet Res Ctr, Linkoping, Sweden Glostrup Univ Hosp, Dept Pediat, Glostrup, Denmark Univ Oxford, Dept Publ Hlth, Oxford, England Med Univ Vienna, Dept Epidemiol, Vienna, Austria Med Univ Silesia, Dept Pediat Endocrinol & Diabet, Katowice, Poland Universidade Federal de São Paulo, Dept Prevent Med, São Paulo, Brazil Natl Taiwan Univ Hosp, Dept Internal Med, Taipei 100, Taiwan Univ Sydney, Kolling Inst Med Res, Sydney, NSW 2006, Australia Univ Leeds, Paediat Epidemiol Grp, Leeds, W Yorkshire, England Cardiff Univ, Ctr Occupat & Hlth Psychol, Cardiff, S Glam, Wales Univ Lancaster, Dept Math & Stat, Lancaster, England Riga Stradins Univ, Dept Publ Hlth & Epidemiol, Riga, Latvia Kaunas Univ Med, Inst Endocrinol, Kaunas, Lithuania Univ Belgrade, Sch Med, Inst Epidemiol, Belgrade, Serbia Med Univ Vienna, Dept Paediat, Vienna, Austria Univ Lecce, Dept Social Sci & Commun, I-73100 Lecce, Italy N Paulescu Inst Diabet, Nutr & Metab Dis Clin, Bucharest, Romania Pediat Clin, Luxembourg, Luxembourg Childrens Diabet Ctr, Sofia, Bulgaria Rigshosp, Bartholin Inst, DK-2100 Copenhagen, Denmark Hosp LMU Munich, Inst Occupat & Environm Med, Munich, Germany Hosp LMU Munich, Outpatient Clin Occupat & Environm Med, Munich, Germany Sir Charles Gairdner Hosp, Perth, WA, Australia Universidade Federal de São Paulo, Dept Prevent Med, São Paulo, Brazil Czech Republic Ministry of Education: MSM 0021620814 Department of Health of Taiwan: DOH 90-TD1028 FAPESP: 94/0943-0 Australian National Health and Medical Research Council (NHMRC): 457302 German Research Foundation: HE 234/1-1 Ministry for Science and Technological Development of Serbia: 145084 European Commission Health Information Strand: 2007115 Web of Science