Blood and urine samples were collected from all participants. Serum free T4, TSH, and thyroid peroxidase antibodies (TPOAb) were analyzed with electrochemiluminescence immunoassay. Free T4, TSH, and TPOAb levels were measured using an E- free T4 kit (Cobas e 411, Roche Diagnositics GmbH Mannheim, Germany), E-TSH kit (Cobas e 801, Roche Diagnostics GmbH, Mannheim, Germany), and E-Anti-TPO kit (Cobas e 801, Roche Diagnostics GmbH, Mannheim, Germany). The reference ranges for free T4 and TPOAb were 0.89 to 1.76 ng/mL and 0–34 IU/mL, respectively. As TSH is affected by iodine intake status, and excess iodine is prevalent in Korea [23 (link)], serum TSH levels between 0.62 and 6.68 mIU/L, based on population data [24 (link)], were considered as reference ranges. Urine iodine concentration was measured by inductively coupled plasma mass spectroscopy (ICP-MS: PerkinElmer ICP-MS, Waltham, USA) and was adjusted for creatinine concentration.
Serum total cholesterol, TG, and HDL-cholesterol were measured by enzymatic methods using a commercial kit (Sekisui, Osaka, Japan) with a Hitachi Automatic Analyzer 7600 (Hitachi, Tokyo, Japan). LDL-cholesterol was calculated using the Friedewald formula: LDL-cholesterol = total cholesterol − HDL-cholesterol − (TG/5) [25 (link)]. Non-HDL-cholesterol was calculated by subtracting the quantity of HDL-cholesterol from total cholesterol [26 (link)].
Serum total cholesterol, TG, and HDL-cholesterol were measured by enzymatic methods using a commercial kit (Sekisui, Osaka, Japan) with a Hitachi Automatic Analyzer 7600 (Hitachi, Tokyo, Japan). LDL-cholesterol was calculated using the Friedewald formula: LDL-cholesterol = total cholesterol − HDL-cholesterol − (TG/5) [25 (link)]. Non-HDL-cholesterol was calculated by subtracting the quantity of HDL-cholesterol from total cholesterol [26 (link)].
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