Prevalence of thyroid diseases in Nevada counties with respect to perchlorate in drinking water

Perchlorate is well-known to inhibit the uptake of iodine by the thyroid an d has been shown to do so at doses in the milligrams-per-day range and high er. Perchlorate has been found in the water supply of Clark County (Las Veg as), Nevada, at 4 to 24 mug/L (karts pm billion) and may provide exposure d osages in the tens of micrograms pm day. An analysis of the Medicaid databa se from Nevada was undertaken to determine whether an increase in the preva lence of any thyroid disease was associated with that level of perchlorate content. The prevalence of pet-sons being seen for thyroid disease or for s pecific thyroid diseases (goiter; nodule, thyrotoxicosis, congenital hypoth yroidism, acquired hypothyroidism, thyroiditis, and other thyroid disorders ) and for thyroid cancer among the Medical-eligible population of each coun ty was calculated for the 2-year period 1997 to 1998. The prevalences in Cl ark County were compared with those in Washoe County tie, Reno), the second most populous county in the state, and with those for the rest Of the stat e. There was no evidence of an increased rate of thyroid disease (or of any specific thyroid disease) associated with perchlorate exposure. Generally: , the prevalences in the metropolitan parts of the state were lower than fo r the rest of the state, particularly for acquired hypothyroidism. This ana lysis found no evidence that perchlorate-containing drinking water at the g iven level increased the prevalence of acquired hypothyroidism or of any ot her thyroid condition.