Does the risk of childhood diabetes mellitus require revision of the guideline values for nitrate in drinking water?

In recent years, several studies have addressed a possible relationship bet ween nitrate exposure and childhood type 1 insulin-dependent diabetes melli tus. The present ecologic study describes a possible relation between the i ncidence of type 1 diabetes and nitrate levels in drinking water in The Net herlands, and evaluates whether the World Health Organization and the Europ ean Commission standard for nitrate in drinking water (50 mg/L is adequate to prevent risk of this disease. During 1993-1995 in The Netherlands, 1,104 cases of type 1 diabetes were diagnosed in children 0-14 years of age. We were able to use 1,064 of these cases in a total of 2,829,020 children in t his analysis. We classified mean nitrate levels in drinking water in 3,932 postal code areas in The Netherlands in 1991-1995 into two exposure categor ies. One category was based on equal numbers of children exposed to differe nt nitrate levels (0.25-2.08, 2.10-6.42, and 6.44-41.19 mg/L nitrate); the other was based on cut-off values of 10 and 25 mg/L nitrate. We determined standardized incidence ratios (SIRs) for type 1 diabetes in subgroups of th e 2,829,020 children with respect to both nitrate exposure categories, sex, and age and as compared in univariate analysis using the chi-square test f or trend. We compared the incidence rate ratios (IRRs) by multivariate anal ysis in a Poisson regression model. We found an effect of increasing age of the children on incidence of type 1 diabetes, but we did not find an effec t of sex or of nitrate concentration in drinking water using the two exposu re categories. For nitrate levels > 25 mg/L, an increased SIR and an increa sed IRR of 1.46 were observed; however, this increase was not statistically significant, probably because of the small number of cases (15 of 1,064). We concluded that there is no convincing evidence that nitrate in drinking water at current exposure levels is a risk factor for childhood type 1 diab etes mellitus in The Netherlands, although a threshold value > 25 mg/L for the occurrence of this disease can not be excluded. Key words: drinking wat er, guideline values, nitrate, type 1 diabetes.