Low dose ionizing radiation exposure and risk of thyroid functional alterations in healthcare workers

To evaluate the possible role of occupational low dose ionizing radiation exposure in increasing the healthcare workers' risk of thyroid functional alterations.

120 healthcare workers exposed to ionizing radiation (60 belonging to category A with a potential exposure to an annual dose between 6 and 20 mSv and 60 to category B potentially exposed to an annual dose between 1 and 6 mSv) were compared with a control group consisting of 60 unexposed healthcare subjects assessing serum levels of different thyroid function parameters as free triiodothyronine, free thyroxine, thyroid stimulating hormone and thyroid autoantibodies. Age, gender, history of thyroid diseases, job task, dosimetric values were analysed as possible influencing factors using linear and multiple logistic regression analysis.

Exposed workers showed significantly higher average levels of thyroid stimulating hormone, and lower average levels of free triiodothyronine and free thyroxine than non-exposed workers, although nonsignificant differences were observed between the two different exposure categories. According to the values of the thyroid hormones a condition of hypothyroidism has been considered in 11 exposed workers (9.2 %) and interestingly this clinical condition was significantly associated with ionizing radiation exposure.

Low dose ionizing radiation exposure would seem to significantly influence levels of free triiodothyronine, free thyroxine, thyroid stimulating hormone, then suggesting a possible increased risk of hypothyroidism in healthcare workers although no relationship could be determined with exposure category. However, further studies are necessary to confirm such association on greater number of workers in order also to define a possible dose-response relationship.