Thyroid function in lead smelter workers: absence of subacute or cumulative effects with moderate lead burdens

To evaluate the effect of low to moderate occupational lead exposure on thyroid function we conducted a cross-sectional study of 151 male lead smelter workers.

Parameters of thyroid function were assessed in relation to both subacute and cumulative lead exposure over a 10-year employment period. Blood lead levels, obtained from plant surveillance records, were used to establish four ordinal levels of current and cumulative exposure (< 15, 15-24, 25-39, and > or =40 microg/dl).

Mean values for the lowest as compared with the highest current exposure group were similar for thyroxine (T4: 6.8 versus 6.1 microg/dl), estimated free thyroxine (EFT4: 1.6 ng/dl in both groups), and thyroid-stimulating hormone (TSH: 1.8 versus 1.7 mIU/l); there was no evidence of a significant trend for diminished thyroid function associated with increasing current lead exposure. Similarly, no significant difference was observed for T4, EFT4, or TSH in relation to the 10-year cumulative exposure or for adjusted analyses controlling for potential confounders, including age and alcohol use.

In contrast to studies observing thyroid dysfunction in the setting of high lead exposure and related clinical poisoning, our findings weigh against a significant physiologic effect on thyroid function at lower levels (< 60 microg/dl) of occupational lead exposure.