Nitrate From Drinking Water and Prevalence of Abnormal Thyroid Conditions Among the Old Order Amish in Pennsylvania

Abstract

PP-31-193 Background/Aims: Nitrate is a widespread contaminant of drinking water, especially in agricultural areas. At high concentrations, ingested nitrate interferes with iodide uptake by the thyroid; thus, potentially impacting thyroid function. Methods: We conducted a cross-sectional study of drinking water nitrate concentrations and thyroid conditions among 2543 old order Amish residing in Lancaster, Chester, Lebanon Counties, Pennsylvania. Thyroid stimulating hormone (TSH) levels, an indicator of thyroid function, were measured from 1995 to 2008 and were used to define the following outcomes: clinical hyperthyroidism (n = 10), clinical hypothyroidism (n = 56), subclinical hyperthyroidism (n = 25), and subclinical hypothyroidism (n = 228). We obtained nitrate concentrations for private wells in these counties that were previously measured (1976–2006) by the US Geological Survey. We estimated nitrate concentrations at study participants' residences using a standard linear mixed effects model that included hydrogeological covariates (aquifer type and land use) and kriging of the wells' residuals. The residual value for each study participant included a weighted average of the 20 neighboring wells. Generalized linear regression was used to assess the relationship between nitrate exposure estimates and thyroid disease status. Results: Nitrate levels estimated by the model ranged from 0.35 mg/L to 16.4 mg/L N-NO3, with a median value of 6.5 mg/L, which we used to define high and low nitrate exposure. Among women, high drinking water nitrate exposure was significantly associated with subclinical hypothyroidism (Odds Ratio = 1.60; 95% Confidence Interval: 1.11–2.32). Nitrate was not associated with subclinical hypothyroidism in men (Odds Ratio = 0.98; 95% Confidence Interval: 0.63–1.52) or with clinical thyroid disease in men or women. Conclusion: Although these data do not provide strong support for an association between nitrate in drinking water and thyroid disease, our results suggest that further exploration of this hypothesis in studies that incorporate measures of both dietary and drinking water nitrate intake are warranted.