Correlation between serum thyroid-stimulating hormone and blood lipid in subjects with normal thyroid function

Objective To investigate the relationship between serum thyroid-stimulating hormone and blood lipid in the population with normal thyroid function. Methods A total of 2 754 participants who underwent a medical examination at the Medical Center of Beijing Chao-yang Hospital were selected as research subjects between April 2018 and April 2019. The free triiodothyronine (FT3), free thyroxine (FT4), TSH, total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C) and low-density lipid Protein cholesterol (LDL-C) levels were tested. TSH, FT3, and FT4 were all within the reference range. General clinical data and lipid levels were compared between male and female populations. The participants were divided into three groups. TSH of the normal high value group was higher than 1.69 while that of the normal low value group was lower than 1.0. The range between 1.0 and 1.9 is defined as the normal median group. The differences of serum lipid levels in different populations were compared under different TSH levels. Multiple linear regression was to analyze the correlation between TSH level and various lipid levels. Results The proportion of smoking, hypertension and diabetes of the male population, and BMI, FT3, FT4, TG levels of the male population were significantly higher than those of the female population, while the age, TSH, TC, HDL-C of the male population were significantly lower than those of the female population (P<0.01). In the total population, the HDL-C level in the TSH normal high value group was higher than the normal median group and the TC level in the TSH normal high value group was higher than in the normal median group and the normal low value group (P<0.05). In the female population, the levels of TG in the normal high value group and the normal median group were higher than in the normal low value group and it was higher in the normal high value group than in the normal median group (P<0.05). The multiple linear regression analysis showed that the TSH level was positively correlated with TC and TG and this correlation was independent of thyroid hormone (β=0.056, P=0.010; β=0.075, P=0.004). Conclusions In the population with normal thyroid function, TSH level was positively correlated with TC and TG. The increase in TSH level within the normal range may be a risk factor for the elevated blood lipids. Key words: Thyrotropin; Blood lipids; Total cholesterol; Triglycerides