Childhood Type 1 diabetes mellitus and parental occupations involving social mixing and infectious contacts: two population-based case-control studies

Aims To test the hypothesis that increased exposure to infections, through parental jobs involving high levels of social mixing, reduces the risk of c hildhood Type 1 diabetes mellitus. Methods Two population-based case-control studies of children diagnosed wit h Type 1 diabetes mellitus from Yorkshire (0-15 years) and Northern Ireland (0-14 years) included 220 and 189 cases and 433 and 465 controls, respecti vely. Parental occupations were coded using a standard occupational classif ication. Each job was allocated to high, medium or low levels of social mix ing according to a predefined categorization. Odds ratios (OR) for the risk of childhood Type 1 diabetes were estimated for parental social mixing by age at diagnosis. Results Childhood Type 1 diabetes mellitus was not associated with high lev els of parental occupational social mixing (Yorkshire - mothers: OR 1.07, 9 5% confidence interval (CI) 0.76-1.50; fathers: 1.15, 0.75-1.76; Northern I reland - heads of household, usually the father: 0.78, 0.49-1.25). A larger proportion of mothers (39%) compared to fathers (18% Yorkshire, 17% Northe rn Ireland) had jobs involving high levels of social mixing. Mothers with h igh social mixing jobs conferred a nonsignificant reduced risk of Type 1 di abetes among children diagnosed under 5 years of age (0.58, 0.24-1.38) comp ared to those diagnosed at age 5 years and above (1.14, 0.77-1.69). Conclusions No association between parental occupational social mixing and the risk of childhood Type 1 diabetes mellitus was detected for all ages co mbined. Mothers were more likely to have jobs involving high levels of soci al mixing than fathers. The possible protective effect of maternal high occ upational social mixing on children diagnosed below 5 years of age merits f urther investigation.