Dyslipidemia in thyroid dysfunction is mostly attributed to thyrotropin (TSH) levels, especially in subclinical disorders, but the exact role of TSH in dyslipidemia has not been explained. A total of 3 020 subjects who remained euthyroid in 3 phases of the Tehran Thyroid study were enrolled and divided according to quartiles of TSH as: Q1 (0.32-1.02), Q2 (1.02-1.53), Q3 (1.53-2.27), and Q4 (2.27-5.06). General Linear model was used to determine whether there was a significant correlation between subjects' lipid profile and quartiles of TSH from 1st to 2nd and from 1st to 3rd phase. Mean TC, LDL-C level and median TG were significantly higher for Q1 in all study phases. All lipid parameters of participants after 6 years (3rd phase study) except LDL-C were significantly varied in different TSH groups. Highest levels of TC, TG and HDL-C were observed in Q4. Thus, irrespective of TC and LDL-C in Q1 and Q4 (participants with the lowest and highest limit of TSH within the normal range), the difference in lipid parameters in middle of normal TSH range was not significant. Normal range TSH levels have a statistically significant effect on lipid profile, but the effect size is not clinically significant.
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