Association Between Thyroid Hormones and Lipids Stratified by Race and Sex

It has been well-established that thyroid hormones play a role in cholesterol and lipoprotein metabolism. However, there is limited data assessing the variability in the association between thyroid hormones and lipids across sex and race. We hypothesized that thyroid dysfunction is associated with changes in lipids and lipoproteins with no substantial variability in this association between races and sex. The electronic medical record of a large county hospital in Dallas, TX was queried to obtain data on all patients who had lipid panels and thyroid function tests checked on the same day from 1/1/2013 to 1/1/2018. The results were stratified into hypothyroid (TSH greater than 4.5 mcIU/L and Free T4 less than 0.8 ng/dL), hyperthyroid (TSH less than 0.5 mcIU/L and Free T4 greater than 1.8 ng/dL) and normal (TSH between 0.5 and 4.5 mcIU/L, Free T4 between 0.8 and 1.8 ng/dL). Results consistent with subclinical thyroid disease were excluded from further analysis. There were 25,290 unique results for thyroid hormones and lipid panels checked on the same day. The results were further stratified by race and sex, and the relationship between thyroid function and lipids was assessed. The correlation coefficient (r) was compared between sexes within each race for the following variables: TSH vs HDL-C, TSH vs LDL-C, TSH vs Total Cholesterol, TSH vs triglycerides, FT4 vs HDL-C, FT4 vs LDL-C, FT4 vs Total Cholesterol, and FT4 vs triglycerides. Among black males with hypothyroidism, there was a notably stronger correlation when compared to black females in the relationship between TSH vs LDL-C, and TSH vs Total Cholesterol. Specifically, the correlation coefficient of TSH vs LDL-C among Black males with hypothyroidism was 0.582, compared to 0.133 among Black females with hypothyroidism (P=0.0053). Furthermore, the correlation coefficient of TSH vs Total Cholesterol among Black males was 0.567 compared to 0.184 among Black females (P=0.016). In contrast, no difference in any of the relationships between thyroid and lipids was demonstrated between sexes amongst Whites, Asians, and Hispanics. Overall, we found differences in Black patients compared to patients of other races with regards to the association between thyroid and lipids. Specifically, it was found that Black males with hypothyroidism had a stronger positive correlation in TSH vs LDL-C and TSH vs Total Cholesterol than Black females. This type of difference between sexes was not found amongst any other race. These findings suggest that thyroid dysfunction is associated with changes in lipids, and the way these changes manifest may vary depending on the race and sex. This further highlights the importance of checking lipid panels in patients with thyroid dysfunction. Further research is needed to more clearly characterize the variation that is seen in thyroid and lipid function amongst races.