The Risk of Type 1 Diabetes Among Offspring of Immigrant Mothers In
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934 Diabetes Care Volume 38, May 2015 Hozan Ismael Hussen,1 Tahereh Moradi,1,2 The Risk of Type 1 Diabetes Among and Martina Persson3 Offspring of Immigrant Mothers in Relation to the Duration of Residency in Sweden Diabetes Care 2015;38:934–936 | DOI: 10.2337/dc14-2348 OBJECTIVE The risk for type 1 diabetes mellitus (T1DM) is increased in the second compared with the first generation of immigrants in Sweden. We investigated the effect of the mother’s duration of stay in Sweden on the risk of T1DM in the offspring. RESEARCH DESIGN AND METHODS Using data from national registries, we identified all subjects with T1DM among 984,798 children born in Sweden (aged 0–18 years) between 1992 and 2009. In- cidence rate ratios (IRRs) with 95% CI were estimated using Poisson regression. RESULTS Offspring of mothers living in Sweden for up to 5 years had a 22% lower risk of T1DM (adjusted IRR 0.78, 95% CI 0.63–0.96) compared with offspring of mothers living in Sweden for 11 years or more. The risk increased with the mother’s duration of stay in Sweden. CONCLUSIONS Our findings support the hypothesis that immigration to Sweden is associated with exposure to new environmental factors that contribute to the development of T1DM in genetically susceptible individuals. The incidence of type 1 diabetes mellitus (T1DM) varies greatly between countries and different ethnic groups (1). This is likely a reflection of differences in genetic 1Department of Environmental Medicine, Division susceptibility and environmental exposures between populations. Sweden has one of Epidemiology, Unit of Cardiovascular Epidemi- of the highest reported incidences of T1DM in the world (2). In Sweden, offspring of ology, Karolinska Institutet, Stockholm, Sweden 2Centre for Epidemiology and Social Medicine, immigrants from most parts of the world have a decreased risk of T1DM compared Health Care Services, Stockholm County Council, NOVEL COMMUNICATIONS IN DIABETES with native Swedes (3). However, the risk of T1DM is increased in offspring of Stockholm, Sweden immigrants from Eastern Africa (4). A number of environmental factors have been 3Department of Medicine, Clinical Epidemiology suggested to contribute to the development of T1DM in genetically susceptible Unit, Karolinska University Hospital, Stockholm, individuals (5–8). Immigration, will by necessity lead to a change in certain environ- Sweden mental exposures. Investigation of the effect of exposure to a new environment on Corresponding author: Martina Persson, martina. [email protected]. the risk for T1DM in different immigrant groups could hopefully add new informa- tion on the gene-environment interaction for the development of T1DM. Received 6 October 2014 and accepted 18 January 2015. This nationwide cohort study analyzed the risk of T1DM in offspring of immigrants © 2015 by the American Diabetes Association. in relation to the number of years the mother had lived in Sweden before the baby Readers may use this article as long as the work was born. We hypothesized that the risk of T1DM in the offspring of immigrant is properly cited, the use is educational and not mothers would increase with their duration of stay in Sweden. for profit, and the work is not altered. Hussen and Associates 935 Table 1—IRR and 95% CI of T1DM among children and young adults (aged 0–18 years) born in Sweden between years 1992 and 2004 and followed until 2009 by maternal duration of residence in Sweden before the child’s birth and parental country of birth IRR* (95% CI) IRR** (95% CI) Duration of residence of mothers before child’s birth Duration of residence of mothers before child’sbirth 0–5 years 6–10 years $11 years Swedes 0–5 years 6–10 years $11 years Swedes Parental migration status Foreign born vs. Swedes† 0.54 (0.47–0.63) 0.69 (0.56–0.84) 0.71 (0.61–0.83) 1 0.55 (0.48–0.64) 0.69 (0.57–0.85) 0.71 (0.62–0.83) 1 Foreign born†† 0.77 (0.62–0.94) 0.98 (0.76–1.25) 1 0.78 (0.63–0.96) 0.96 (0.75–1.24) 1 East African vs. Swedes† 1.03 (0.72–1.46) 1.39 (0.86–2.24) 2.34 (1.30–4.24) 1 1.00 (0.70–1.42) 1.32 (0.82–2.14) 2.27 (1.25–4.10) 1 East African†† 0.36 (0.17–0.75) 0.48 (0.21–1.09) 1 0.39 (0.17–0.86) 0.49 (0.21–1.12) 1 Other Nordic vs. Sweden† 0.85 (0.54–1.33) 1.11 (0.69–1.78) 1.07 (0.87–1.32) 1 0.88 (0.56–1.38) 1.13 (0.70–1.81) 1.08 (0.88–1.33) 1 Other Nordic†† 1.11 (0.43–2.86) 1.34 (0.44–4.04) 1 0.94 (0.34–2.55) 1.22 (0.40–3.75) 1 The study base comprised 1,263,358 individuals. Exclusions: infants delivered before 28th or after 43rd completed weeks of gestation, from multiple births, with any congenital malformation, individuals with missing data on gestational age, missing data on birth weight, infants with a birth weight 6 6 standard deviations from the mean, records with missing or extreme data on maternal height, weight, and age, and women with invalid immigration. The final cohort comprised 984,798 eligible individuals. *Adjusted for child’s age at follow-up. **Adjusted for maternal age, maternal BMI, smoking at enrollment, parental education, parity, preeclampsia, and child’s sex and age at follow-up. †Swedes as a reference. ††Longest duration of stay as a reference. 10 – ned fi rst. 5years,6 ned as foreign fi – fi ), emigration, sbirth.Parental ’ 1996 and ICD-10: – rst de nal cohort comprised fi ed in the national pa- ed by parental country fi ed into 0 fi fi fi 18 years, born and living – 11 years. Risk estimates $ sbirth,classi ’ 18 years, identi The outcome of interest was de All statistical analyses were per- Themainexposurevariablewasmater- rst trimester BMI, maternal smoking, – years, and were adjusted for maternal age atfi delivery, parental education, parity, preeclampsia, birthweight,andsexandageofthechild at follow-up. tient registry according to thetenth ninth and Swedish versions ofcode 250 ICD between (ICD-9 1987ICD-10 and code 1996, E10 and from 1997 onwards). formed with SAS 9.3stitute, software Inc., Cary, (SAS NC). In- as a diagnosis of T1DM0 in children aged RESULTS During the study periodand between 2009, 1992 4,825 cases of T1DM were Statistical Analysis Using Poisson regression models,culated we incidence cal- rate ratios (IRRs)95% with CI to estimatethe the offspring, strati risk of T1DM in born (both parents born abroad).ther We categorized fur- parents as ofrents Nordic born (pa- in Finland,and Iceland) Norway, and East Denmark, African (parents born in East African countries) origin. nal duration of staychild in Sweden before the Follow-up The cohort members were followed from the date of birth between 1992 anduntil 2004 the date ofcording diagnosis to of T1DM the ac- SwedishICD versions (ICD-9: 250, of 1987 the death, or end of follow-up (31 December 2009), whichever occurred of birth and maternal duration of residency in Sweden before the child country of birth was Study Cohort The study base consisted of 1,263,358 in- dividuals aged 0 in Sweden any time1992 between and 31 1 December 2004. January After exclu- sions (Table 1), the 984,798 eligible individuals. E10, 1997 and onwards RESEARCH DESIGN AND METHODS Database We used data fromset, a The nationwide Migration data and(9), Health which Cohort is thevariety result of of Swedish linkage nationaldemographic of registers. health a and care.diabetesjournals.org 936 Mother’s Duration of Stay and T1DM in Offspring Diabetes Care Volume 38, May 2015 diagnosed among 984,798 Sweden-born Exposure to viral infections and early full access to all the data in the study and takes children between 0 and 18 years of age; introduction of certain nutrients, such as responsibility for the integrity of the data and of these, 474 children were offspring of cow’s milk and gluten, may contribute to the accuracy of the data analysis. immigrant mothers. Offspring of moth- the development of T1DM in the geneti- References ers living in Sweden for up to 5 years cally susceptible individual (5,10). Data 1. Karvonen M, Viik-Kajander M, Moltchanova had a 22% lower risk of T1DM (IRR also indicate that different exposures E, Libman I, LaPorte R, Tuomilehto J. Incidence 0.78, 95% CI 0.63–0.96; Table 1) com- may interact and increase the risk for of childhood type 1 diabetes worldwide. Diabe- pared with offspring of mothers living T1DM even further (11). In Sweden, the tes Mondiale (DiaMond) Project Group. Diabe- in Sweden for at least 11 years. The cold climate with increased time spent tes Care 2000;23:1516–1526 risk of T1DM in offspring of immigrants indoors may facilitate the spread of viral 2. DIAMOND Project Group. Incidence and trends of childhood type 1 diabetes worldwide increased with increasing duration of infections, and the consumption of milk 1990-1999. Diabet Med 2006;23:857–866 the mother’s stay in Sweden. Offspring products and gluten is high. The finding of 3. Hussen HI, Yang D, Cnattingius S, Moradi T. of mothers from eastern Africa had the increasing risks of T1DM in the offspring Type I diabetes among children and young adults: same risk pattern with increasing risks of immigrants with length of stay in Swe- the role of country of birth, socioeconomic posi- – with longer duration of stay.