Correlation Analysis Of Thyroid Function Indicators And Lipids As Well As Fatty Liver

Objective: Over the past few decades,the associations of thyroid function and serum lipids as well as fatty liver(FL)have been extensively studied,leading to inconsistent results.Recent evidence suggests that if the relationship can be analyzed based on the theory of thyroid hormone resistance,these contradictory results may be reasonably explained.This study aimed to investigate the association of single functional indices [free triiodothyronine(FT3),free thyroxine(FT4)and thyroid stimulating hormone(TSH)] and composite functional indices [FT3 to FT4 ratio(FT3/FT4)and thyroid feedback quantilebased index(TFQI)] of the thyroid system and serum lipids as well as FL.The relationships between subclinical thyroid dysfunction and serum lipids as well as FL were also analyzed.Methods: We retrospectively reviewed the medical charts of 7,689 subjects who attended a routine health check-up at the First Hospital of China Medical University from January2017 to December 2018.Data regarding the subjects’ baseline characteristics were collected.All subjects were categorized into two groups according to whether there was dyslipidemia or FL and all indexes were compared.FT3,FT4,TSH were measured by electrochemical luminescence immunoassay.Peripheral sensitivity to thyroid hormones was evaluated by the FT3/FT4.TFQI(FT4)was calculated to evaluate central sensitivity to thyroid hormones.TFQI(FT3)was obtained by replacing the FT4 in the formula with FT3.Kendall’s tau-b correlation and binary logistic regression models were used to evaluate the associations of single and composite functional indices of the thyroid system with serum lipids as well as FL.Results: Compared to tertile 1,tertile 3 of FT3/FT4 levels were associated with 1.58-folds(95% confidence interval [CI],1.33-1.86,P for trend < 0.001)increased risk of high TG;1.31-folds(95% CI,1.13-1.53,P for trend = 0.001)increased risk of high TC;1.25-folds(95% CI,1.07-1.46,P for trend = 0.006)increased risk of high LDL-C;and 1.44-folds(95%CI,1.20-1.73,P for trend < 0.001)increased risk of FL after adjustment for confounders.Similarly,compared to tertile 1,tertile 3 of TFQI(FT3)levels were associated with 1.57-folds(95% confidence interval [CI],1.33-1.86,P for trend < 0.001)increased risk of high TG;1.31-folds(95% CI,1.12-1.53,P for trend = 0.001)increased risk of high TC;1.25-folds(95% CI,1.07-1.46,P for trend = 0.006)increased risk of high LDL-C;and 1.44-folds(95% CI,1.20-1.73,P for trend < 0.001)increased risk of FL after full adjustment.Subgroup analysis showed that subclinical hyperthyroidism was negatively correlated with the risk of high TC and high LDL-C(OR 0.44,95%CI 0.20-0.94,P = 0.033;OR 0.37,95%CI 0.16-0.84,P = 0.018,respectively).Subclinical hypothyroidism was positively correlated with the risk of high TC,high TG and high LDL-C(OR 1.84,95%CI 1.07-3.16,P = 0.027;OR 2.01,95%CI 1.10-3.65,P = 0.022;OR 1.79,95%CI 1.04-3.07,P = 0.036).However,no significant association between subclinical thyroid dysfunction and FL was detected(subclinical hyperthyroidism: P = 0.160;subclinical hypothyroidism: P = 0.224,respectively).Conclusions: We have shown that thyroid function indicators were closely related to serum lipids.TFQI(FT3)may be a new indicator to assess the relationship between thyroid function and lipids as well as FL.Subclinical thyroid dysfunction was not associated with FL.