Thyroid function and lead: no clear relationship.

It has been suggested that the nonspecific symptoms of inorganic lead intoxication are related to the effects of the blood lead on thyroid function. A cross-sectional study of the thyroid function status of a stable work force with long-term exposure to inorganic lead was conducted. No statistically significant relationship between blood lead and thyroxine (T4) or an estimate of "free T4" was identified. These results and those of another recent study cast doubt on the existence of any direct, easily identifiable relationship between moderate blood lead level elevations and the usual measurements of thyroid function.