Du X, et al. - Researchers studied 289 thyroid nodules cases and 109 healthy subjects (control group) admitted to the Hebei General Hospital to investigate the connection between serum 25 hydroxyvitamin D3(25(OH)D3) and insulin-like growth factor-1 (IGF-1) and thyroid nodules. Electrochemiluminescence and radioimmunoassay methods detected serum 25(OH) D3 and serum IGF-1, respectively. Between the nodules group and the control group, serum 25(OH)D3, IGF-1, fasting blood glucose, total cholesterol, waist circumference, total triiodothyronine, total thyroxine, history of hypertension, and history of drinking were significantly different. With a high-level serum 25(OH)D3, the incidence of thyroid nodules is comparatively reduced; serum 25(OH)D3 could be a directly protective in thyroid nodules. Another one of the indirect thyroid nodular protective factors may be serum IGF-1.