Diabetes and Drinking Water.

Exploring the Connection to Nitrate

Several recent studies have correlated nitrate in drinking water with the incidence of type 1 diabetes mellitus. Given a sharp increase in type 1 diabetes in the Netherlands, Jan M. S. van Maanen and colleagues attemped to clarify the possible nitrate-diabetes relationship. Their results show no convincing evidence that nitrate in drinking water at concentrations of 25 milligrams per liter (mg/L) or less is a risk factor for the disease, although a link at higher concentrations cannot be excluded [EHP 108:461-465].

The human body transforms nitrate to nitrite. Nitrite may also react with amines in the digestive juices to form N-nitroso compounds. N-nitroso compounds have been shown to attack pancreatic cells in animals, causing diabetes. Studies in the United Kingdom and United States have linked nitrate in water to type 1 diabetes, while studies in Sweden and Finland have shown a dose-response relationship between type 1 diabetes and foods rich in nitrate, nitrite, and nitrosamines.

In the Netherlands the incidence of type 1 diabetes among children 0-4 years old doubled between 1990 and 1995, and the overall incidence in children aged 0-14 years increased 32% between 1980 and 1995, from 11.1 to 14.6 cases per 100,000. Nitrate concentrations in drinking water are tracked in every postal code in the Netherlands. In their ecological and epidemiological study, the authors sorted by postal code the cases of 1,064 children aged 0-14 years who had been diagnosed with type 1 diabetes between 1993 and 1995. They then compared the incidence of diabetes to nitrate exposure as indicated by the water records.

The study found a correlation between increasing age and the incidence of type 1 diabetes, but no convincing evidence of a link between nitrate exposure and diabetes. Study results do indicate a possible correlation between diabetes risk and nitrate concentrations above 25 mg/L, but the number of children exposed to these concentrations was so small that the results are not statistically significant.

Only 1% of the children in the study were exposed to nitrate concentrations above 25 mg/L, and 18% to concentrations above 10 mg/L, in contrast to a U.K. study where 33% of children were exposed to concentrations above 15 mg/L. The U.K. study linked nitrate concentrations and diabetes at a threshold of 15 mg/L, while the Dutch study did not. The Dutch study was also unable to substantiate a U.S. study that indicated a risk threshold of 10 mg/L.

The authors conclude that more studies are needed to evaluate the possible role of environmental factors in the increase of type 1 diabetes in the Netherlands and to more accurately determine safe concentrations of nitrate in drinking water. According to the authors, the present World Health Organization maximum permissible level of 50 mg/L for nitrate in drinking water may not be adequate to prevent risk of diabetes.