Relationship between metabolic syndrome and nodular thyroid diseases.

Nodular thyroid diseases are common in Turkey. Insulin resistance (IR) is considered as the most important component of metabolic syndrome (MetS), and it is thought to directly affect thyroid diseases, together with other components of MetS. The aim of this study was to evaluate potential factors associated with thyroid nodularity. This study was part of the prospective MELEN study. In total, randomly selected 2233 subjects were evaluated. A euthyroid subgroup of participants (n = 1432) was selected and 421 of them had MetS. Both goitres and multinodular goitres (MNGs) were significantly more common in the MetS (+) group (p < .001). Older age was the only factor that significantly affected the presence of a nodular goitre (NG) (p < .001). The presence of a MNG was associated with older age (p < .001), systolic blood pressure level (p < .008) and MetS (p < .001). There was no difference in the thyroid volume or presence of nodular thyroid diseases between the IR (+) and (-) groups. Both the thyroid volume and the presence of MNGs were significantly associated with MetS, independent of thyroid-stimulating hormone (TSH) and IR. We suggest that the individual components of MetS may influence thyroid nodularity to some degree and that together they exert a cumulative effect on the thyroid gland. As a result, in the absence of MetS, we further suggest that IR alone does not explain the increase in thyroid volume and thyroid nodule formation.