Effects of Thyrotrophin, Thyroid Hormones and Thyroid Antibodies on Metabolic Parameters in a Euthyroid Population With Obesity

Sule Temizkan; Bilgken Balaforlou; Aysenur Ozderya; Mehmet Avci; Kadriye Aydin; Selin Karaman; Mehmet Sargin

Disclosures

Clin Endocrinol. 2016;85(4):616-623. 

In This Article

Results

General Characteristics, Thyroid Function and Metabolic Measures of the Obese Population

Of 5300 subjects with obesity, 1275 subjects who met the inclusion criteria were recruited for this study. Eighty-three per cent (n = 1063) of the study population were women. The mean age of the study population was 38 ± 11 years and mean BMI was 37 ± 5 kg/m2. The median TSH of the study population was 1·9 (1·3–2·5). Anti-TPO positivity was 14%, and anti-TG positivity was 15%. TSH and anti-TPO positivity were significantly higher in women than in men [1·9 (1·3–2·6) vs 1·7 (1·2–2·3); P = 0·005 and 15% vs 10%; P = 0·03, respectively]. The median HOMA-IR of the study population was 3·5 (2·5 5·1) (Table 1). The median TSH was 1·8 μIU/ml (1·3 2·4) in antibody-negative subjects with obesity and 2·1 μIU/ml (1·4 2·9) in antibody-positive subjects (P < 0·001). FT3 was similar in antibody-negative and antibody-positive groups (P = 0·60); however, FT4 was lower in the antibody-positive group (P = 0·006). BMI and PBF were similar in antibody-positive and antibody-negative groups (data not shown in table). Figure 1 shows the comparison of HOMA-IR and TC/HDL-C ratio of the study population with or without thyroid autoantibodies. HOMA-IR and TC/HDL-C ratios were not significantly different in antibody-positive and antibody-negative subjects with obesity (P = 0·58 and P = 0·66, respectively). P was derived from ancova and adjusted for age, gender, BMI, smoking status, TSH, FT3 and FT4.

Figure 1.

Comparison of HOMA-IR and TC/HDL-C ratio of the study population with or without thyroid autoantibodies. P derived from ancova and adjusted for age, gender, BMI, smoking status, TSH, FT3 and FT4.

Thyrotrophin, Thyroid Hormone Levels and Antibody Positivity in Subjects With Morbid Obesity

Twenty-six per cent (n = 333) of the study population was morbidly obese. Table 2 shows the comparison of thyroid function in subjects with grade I and grade III obesity. In the first group (BMI = 30–34·9 kg/m2; n = 488), mean BMI was 32 ± 2 kg/m2. In the second group (BMI ≥40 kg/m2; n = 333), mean BMI was 44 ± 4 kg/m2. Gender distribution and thyroid antibody positivity were similar in both groups. The inflammatory markers, WBC and CRP were significantly higher in the morbidly obese group (for both, P < 0·001). TSH levels were similar in both BMI groups and unchanged after adjustment for age, gender, smoking status, thyroid antibody positivity, WBC and CRP (P = 0·81). FT3 and FT4 levels were significantly higher in the morbidly obese group, but after adjustment for age, gender, smoking status, thyroid antibody positivity, WBC and CRP, levels were no longer significantly different (P = 0·21 and P = 0·16, respectively). The FT3/FT4 ratio was similar in the two BMI groups (P = 0·57).

Metabolic Parameters According to TSH Quantiles

Two groups were organized based on TSH quantiles (Table 3). The median TSH level of the lower quantile was 1·3 (1·0–1·5), and median TSH level of the upper quantile was 2·5 (2·1 3·2). Gender distribution, BMI, PBF and FT3 were similar in the two groups; however, FT4 and age were significantly lower in the upper TSH quantile. FBG, TC, HDL-C and LDL-C were similar in both groups, even after adjustment for age, gender, BMI, current smoking status, thyroid antibody positivity, FT3 and FT4. FI, HOMA-IR, CRP and WBC were significantly higher in the upper TSH quantile, even after adjustment for age, gender, BMI, current smoking status, thyroid autoantibody positivity, FT3 and FT4 (P = 0·004, P = 0·009, P = 0·01, and P = 0·04, respectively).

Correlation Between Thyrotrophin, Thyroid Hormones, Thyroid Antibodies and Metabolic Measures

Correlation between thyroid function and metabolic parameters in the study population is shown in Table 4. TSH was not correlated with any of the metabolic parameters (BMI, PBF, FBG, HOMA-IR, TC, HDL-C, LDL-C and TG). FT3 was positively correlated with BMI, PBF and HOMA-IR and negatively correlated with FBG, TC, HDL-C and LDL-C. FT4 levels were positively correlated with BMI and PBF and negatively correlated with FBG, HOMA-IR, TC, LDL-C and TG. The FT3/FT4 ratio was positively correlated with FG, HOMA-IR, TC, LDL-C and TG and negatively correlated with PBF. Table 5 shows predictors of IR (HOMA-IR ≥ 2·7) and atherogenic dyslipidaemia (TC/HDL-C ≥ 5). Neither TSH nor thyroid antibody positivity was associated with IR and atherogenic dyslipidaemia. FT3 was positively associated with IR (P < 0·001) and atherogenic dyslipidaemia (P = 0·03); however, this association lost its significance after adjustment for age, gender, BMI and smoking status (Model 2). FT4 was negatively associated with atherogenic dyslipidaemia and this association remained after adjustment for age, gender, BMI and smoking status (P = 0·008; Model 2), but lost its significance after further adjustment for WBC and CRP (P = 0·08; Model 3). FT4 was negatively associated with IR and this association remained even after adjustment for age, gender, BMI, smoking status, WBC and CRP (P < 0·001; Models 2 and 3).

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