Associations between the levels of thyroid hormones and lipid/lipoprotein levels: Data from National Health and Nutrition Examination Survey 2007–2012

Data from National Health and Nutrition Examination Survey for the years 2007–2012 were used to investigate associations between thyroid hormones and lipid/lipoprotein levels for a representative sample of general US population aged ≥20 years. There were no statistically significant differences for adjusted high density lipoprotein levels among thyroid function groups, namely, subclinical hyperthyroid (SCHPR), clinical hyperthyroid (CHPR), euthyroid (EU), clinical hypothyroid (CHYP), and subclinical hypothyroid (SCHYP). For the general US population, positive associations for thyroid stimulating hormones (TSH) and negative associations for free thyroxine (FT4) levels were observed with total cholesterol (TC, p < 0.01), apolipoprotein B (APOB, p < 0.01), and triglycerides (TG, p < 0.01). A 10% increase in TC levels was associated with a 2% increase in TSH levels and 0.8% decrease in FT4 levels. Among EU subjects, TG levels were positively correlated with TSH (p < 0.01) and negatively correlated with FT4 (p < 0.01). For CHYP subjects, TG levels were negatively correlated with TSH (p < 0.01). For iodine deficient participants, low density lipoprotein levels (LDL) were lower for SCHPR when compared with EU or CHYP (p < 0.01). TC levels were usually lower for SCHPR than for EU, CHYP, and SCHYP but the differences were not necessarily statistically significant. For all participants and for iodine replete participants, TG levels for SCHPR were lower than for CHYP (p < 0.01). CHYP and SCHYP had higher levels of TG than other three thyroid function groups. APOB levels were lower for SCHPR than for EU and CHYP for all participants and for iodine replete participants (p < 0.01). There was a positive association between the four quartiles of thyroid stimulating hormones and TC, TG, and APOB. There was also an inverse association between the quartiles of free thyroxine levels and LDL, TC, TG, and APOB.