Association between thyroid function and selected organochlorine pesticides: data from NHANES 2001-2002

Exposure to organochlorine pesticides (OCP) has been shown to be associated with adverse thyroid function. The impact of exposure to selected OCPs on total serum thyroxine (TT4) and thyroid stimulating hormone (TSH) was evaluated by analyzing data from the 2001-2002 National Health and Nutrition Examination Survey. Oxychlordane, p,p'-DDE, trans-nonachlor, and heptachlor epoxide were selected for analysis. Regression models with logs of TSH and TT4 as dependent variables and OCP exposure, race/ethnicity, iodine and smoking status, total lipids and others as independent variables were fitted. TSH levels increased (p < 0.05) with increase in trans-nonachlor exposure for 20-39 year old iodine deficient males. TSH levels were higher when oxychlordane exposure was low than when the exposure was medium or high for 20-39 year old iodine deficient females (p < 0.05). For iodine deficient females, TT4 levels were lower when p,p'-DDE exposure was low than when it was medium (p < 0.05). For non-Hispanic blacks (NHB), TT4 levels decreased with increase in exposure to heptachlor epoxide (p < 0.05). For iodine replete males, TSH levels increased with increase in trans-nonachlor exposure (p < 0.05). For iodine replete females, (i) Mexican Americans (MA) had higher TSH levels when the exposure to oxychlordane was medium than when the exposure was low; (ii) for 60+years old, there was a positive association between TSH and heptachlor epoxide levels; and (iii) TT4 levels had an inverse association with trans-nonachlor and oxychlordane. In general though not always, (i) TSH and TT4 levels were lowest for the 20-39 years old and highest for the 60+years old (p < = 0.05), (ii) TSH and TT4 levels for iodine deficient males and females were lowest for NHB, highest for MA, and in-between for non-Hispanic white, and (iii) non-smokers had higher TSH and TT4 levels than smokers and in general, statistically significantly so.