Objective: To investigate whether higher IDDM incidence rates occurred in areas with high nitrate levels in their potable water supplies.
Research design and methods: Incidence rates for the 63 counties in Colorado were calculated using the Colorado IDDM Registry of children diagnosed < 18 yr of age between 1978 and 1988 (n = 1280). A weighted average of the nitrate levels from each water district within each county was calculated using data collected by the Colorado Department of Health between 1984 and 1988.
Results: The rs between nitrate levels and IDDM incidence was 0.26 (P = 0.03). After controlling for differences in ethnicity, counties with water nitrate levels in the third tertile (0.77-8.2 mg/L) had a significantly increased risk of IDDM compared with those in the first tertile (0.0-0.084 mg/L) (rp = 0.29, P = 0.02).
Conclusions: This ecological analysis suggests that low-level nitrate exposure through drinking water may play a role in the etiology of IDDM, perhaps as a promoter through the generation of free radicals.