Effect of passive smoking on thyroid function in infants

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.