To investigate whether higher IDDM incidence rates occurred in areas with high nitrate levels in their potable water supplies.
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.
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).
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.