Evaluation of diabetes mellitus, serum glucose, and thyroid function amongUnited States workers exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

Objective-Some studies suggest that exposure to 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) may affect glucose metabolism and thyroid function. To furt her assess the relation between exposure to TCDD and endocrine function, da ta from the largest morbidity study of industrial workers exposed to TCDD w ere examined. Methods-A cross sectional study of workers employed >15 years earlier in th e manufacture of 2,4,5-trichlorophenol or one of its derivatives at two Uni ted States chemical plants was conducted. The referent group consisted of p eople with no occupational exposure to phenoxy herbicides and were recruite d from the neighbourhoods where the workers lived. Results-A total of 281 workers and 260 unexposed referents participated. Th e mean current serum lipid adjusted TCDD concentration among workers was 22 0 pg/g lipid, and among referents was 7 pg/g lipid (p<0.05). The half life extrapolated TCDD concentrations (the estimated TCDD concentration when occ upational exposure to TCDD stopped) among workers averaged 1900 pg/g lipid (range: not detected-30 000 pg/g Lipid). Overall, the prevalence of diabete s mellitus was not significantly different between the workers and referent s. Also, there was not a significant positive trend between prevalence of d iabetes and increasing serum TCDD concentration. However, diabetes was foun d in six of 10 (60%) workers with current serum TCDD concentrations >1500 p g/g lipid. After excluding subjects being treated for diabetes, workers in the group with the highest half life extrapolated TCDD concentrations had a significantly increased adjusted mean serum glucose concentration compared with referents (p=0.03). Workers were also found to have a significantly h igher adjusted mean free thyroxine index compared with referents (p=0.02), especially among workers in the group with the highest half life extrapolat ed TCDD concentrations. However, no evidence was found that workers exposed to TCDD were at increased risk of thyroid disease. Conclusions-These findings provide modest evidence that exposure to TCDD ma y affect thyroid function and glucose metabolism.