Objective: To evaluate the effect of passive smoking on thyroid function in infants. Design and methods: Cord serum tri-iodiothyronine (T3), free T3 (fT3), thyroxine (T4), free T4 (fT4), TSH, thyroxine binding globulin (TBG), thyroglobulin (TG) and cord plasma thiocyanate were measured at birth, and serum TG and thiocyanate after 1 year of life, in 18 infants born from parents who did not smoke (group A), in 18 infants with a father who smoked (group B) and in 18 infants with parents both being smokers (group C). Results: No significant differences were observed in cord serum concentrations of T3, fT3, T4, fT4, TSH and TBG among the three groups. Median (range) TG concentrations (ng/ml) were 30.2 (5.0-102.0), 56.3 (20.5- 208.0) and 76.0 (26.0-199.0) at birth (P = 0.009 for groups A and B compared; P = 0.0002 for groups A and C compared), and 14.9 (5.4-32.0), 19.5 (10.0- 57.5) and 20.0 (14.0-40.7) at 1 year (P = 0.017 for groups A and C compared), in the three groups respectively, and thiocyanate concentrations (mmol/1) were 3.3 (0.0-51.4), 12.9 (0.0-122.2) and 27.8 (3.3-184.5) at birth (P = 0.015 for groups A and C compared), and 3.1 (0.0-32.7), 6.0 (0.0-47.3) and 20.3 (0.0-230.8) at 1 year (P = 0.01 for groups A and C compared) in the three groups respectively. Conclusions: TG and thiocyanate concentrations at birth and at 1 year of age in infants of smoking parents are greater than in infants with non-smoking parents. These results indicate that the change in thyroid function as evaluated by serum TG concentrations observed at birth can persist at least for 1 year if the exposure to passive smoking from both parents is continued. Increased TG concentrations may be due to a direct effect of thiocyanate on the thyroid gland.
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