Endocrine Abstracts

Insulin is a thyroid growth factor that stimulates proliferation of thyroid cells in culture. It has been observed that insulin receptors are over expressed in most thyroid tumors as an early step in thyroid carcinogenesis.

Eighty women (mean age 36.85±4.71 years) were evaluated by a thyroid ultrasound (US), fasting plasma insulin and HOMA IR. Subjects were divided into four groups as follows: G1 (n: 24),subjects with IR and obesity; G2 (n: 20), subjects with obesity without IR; G3 (n: 16), subjects with IR and normal weight; and G4 (n: 20) control group (without IR and obesity).

The thyroid volume (TV), measured by US, was in G1, 17.15±1.6 ml; G2, 7.4±1.4 ml; G3, 16.53±1.9 ml; and G4, 6.07±0.95 ml. There was no significant difference in TV between G1 and G3, but differences between G1 and G2, and between G3 and G4 were significant at P<0.05. The percentage of nodular thyroid glands observed by US in each group was as follows: G1, 58%; G2, 15%; G3, 50%; G4, 5%. Again, the differences between G1 and G2 and between G3 and G4 were statistically significant (P<0.005 and P<0.001, respectively, for each comparison). Our study also showed that the greater waist circumference;(as one parameter of insulin resistance syndrome by IDF), the greater thyroid volume and the higher incidence of thyroid nodules.

Conclusions: High circulating levels of insulin cause increased thyroid proliferation resulting in a large thyroid volume and the formation of nodules. Thus, the thyroid gland appears to be another victim of the insulin resistance syndrome.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.