Higher concentrations of arsenic and fluoride in the public drinking water supply in Newfoundland and Labrador may be associated with the high incidence of type 1 diabetes in the Canadian province, according to findings published in BMJ Open Diabetes Research & Care.

Newfoundland and Labrador has the second highest incidence rate of type 1 diabetes in the world after Finland, with an incidence rate of 49.9 per 100,000 for children during the 2007-2010 period (95% CI, 42.2-57.6), Roger Chafe, PhD, associate professor of pediatrics and director of the Janeway Pediatric Research Unit at Memorial University of Newfoundland, St. John’s, Canada, and colleagues wrote in the study background. The highest incidence during 2007-2010 was among children aged 5 to 9 years, they noted, with an incidence rate ratio of 59.1 (95% CI, 45-76.3) for that age group.

“There is accumulating evidence that drinking-water ingredients may be implicated in the environmental exposures contributing to the pathogenesis and progression of type 1 diabetes,” Chafe and colleagues wrote. “Newfoundland and Labrador has one of the highest reported incidences of type 1 diabetes worldwide, and the reasons for these high rates are unknown. The rates of type 1 diabetes are increasing in the province.”

In a community-based, case-control study, Chafe and colleagues analyzed longitudinal data on the incidence rates of type 1 diabetes in 240 communities with a single public water supply monitored by the Provincial Department of Environment and Climate Change between 2000 and 2012. Water quality for each community was averaged during the sampling period to produce one representative value for 21 nutrients and metals and eight major ions, including arsenic, fluoride, barium and nickel. Cases of type 1 diabetes, identified using the Newfoundland and Labrador Pediatric Diabetes Database, were assigned to communities based on self-reported place of residence at the time of diagnosis. Cases occurring in communities not supplied by public water were excluded.

Researchers analyzed the differences in water quality between communities with and without cases of type 1 diabetes using analysis of variance, and used regression analysis to analyze the relationship between water quality and incidence rates of type 1 diabetes at both the community and regional levels, using 89 census consolidated subdivisions.

Researchers observed 499 cases of type 1 diabetes between 2001 and 2012, for an incident rate of 51.7 per 100,000 people for the province during the study period, with 87% of cases occurring in 114 communities serviced by the public water supply. In these communities, the concentration of water nutrients and metals, including ammonia, barium, copper, lead, magnesium, uranium and zinc, were higher vs. communities without diabetes cases, according to researchers.

In regression analysis, researchers found that arsenic level was positively associated with type 1 diabetes incidence at the community level (beta = 0.268; P = .013), as was fluoride level (beta = 0.202; P = .005). In regression analysis at the regional level, barium was negatively associated with diabetes incidence (beta = –0.478; P= .009), as was nickel (beta = –0.354; P = .05). At the regional level, researchers did not observe associations between major ions and diabetes incidence.

“It is also important to note that no component was found to have a significant association across the three different levels of analysis performed,” the researchers wrote. “If any component was significantly associated across all three ways of analyzing the data, it would have made for a stronger case for a wider association with that element in the water supply.”

The researchers added that more experimental and clinical research is needed to elucidate the role of drinking water compounds in the pathophysiology of type 1 diabetes.

Disclosures: The authors report no relevant financial disclosures.

*Original article online at https://www.healio.com/endocrinology/diabetes/news/in-the-journals/%7Bfd47c563-fb04-48cc-a4a6-4b1899ea7676%7D/drinking-water-linked-to-high-type-1-diabetes-rate-in-canadian-province