Background: Thyroid hormones play an important role in lipid metabolism. Overt hypothyroidism is known to be associated with increased lipid profiles, but the effect of subclinical hypothyroidism (SCH) on lipid profile remains controversial.
Objectives: The aim of this study was to assess the association between thyroid disorders and serum lipid levels.
Materials and methods: The present study was conducted within the framework of Tehran lipid and glucose study (TLGS). Serum concentrations of TSH and FT4, cholesterol, triglycerides and HDL-C were measured in 5786 randomly selected subjects. Serum LDL was calculated according to the Friedwald formula.
Results: The study assessed 5154 subjects including 42.5% males and 57.5% females, with a mean age of 39.71 ± 14.2 years (ranged 20 - 90 years). Serum cholesterol was significantly higher in overt hypothyroidism in comparison to subclinical hypothyroidism (P = 0.003). Serum cholesterol, HDL -C, LDL-C and TG did not differ between subclinical hypothyroid and control groups. Among euthyroid men, serum FT4 levels were inversely correlated with serum cholesterol and TG. In euthyroid women, serum FT4 levels were correlated positively with serum HDL-C and negatively correlated with TG and TG/HDL-C ratio and TSH levels were associated negatively with, HDL-C.
Conclusions: No differences existed in lipid profiles between subclinical hypothyroidism and euthyroid subjects. There are correlations between serum FT4 and TSH and lipid profiles.
Keywords: Hypothyroidism; Lipid Profile; Tehran Thyroid Study (TTS); Thyroid.