Endurance training improves heart rate on-kinetics in women with subclinical hypothyroidism: a preliminary study.

PURPOSE: The aim of the study was to evaluate the effect of endurance training on heart rate (HR) on-kinetics in patients with subclinical hypothyroidism (SH). METHODS: Eighteen women were randomly assigned to trained group (TG) or control group (CG). Both groups performed three tests at 50 W in a cycle ergometer for 6 min. HR kinetics was obtained during the tests and the mean response time (MRT), which is equivalent to the time taken to reach 63% of the HR at steady state, was extracted. The TG was then submitted to 12 weeks of endurance training (50 min, 3x/week, intensity between 70 and 85% of the maximum HR predicted for the age). Statistical analysis was performed by the mixed analysis of variance. RESULTS: At baseline, TG and CG were similar for TSH (7.7 ± 3.1 vs. 6.9 ± 3.3 mUI/L, p = 0.602, respectively) and FT4 (12.31 ± 1.51 vs. 12.20 ± 1.89 pmol/L, p = 0.889, respectively). After adjustment for body mass index and age, interactions between moment (baseline or after 12 weeks) and group (trained or control) were only significant for MRT (TG: 39.6 ± 10 to 28.9 ± 8.4 s, CG: 53.6 ± 20.3 to 55 ± 19.7 s, p = 0.001) and physical activity level (CG: 7.3 ± 0.7 to 8 ± 0.9, CG: 6.8 ± 0.8 in both moments, p = 0.005). CONCLUSION: The preliminary results suggest that 12 weeks of endurance training improve HR on-kinetics and physical activity level in SH.

Evaluation of epicardial fat tissue thickness as a marker of cardiovascular risk in patients with subclinical hypothyroidism.

BACKGROUND: Epicardial fat thickness (EFT) has been evaluated as a marker of cardiovascular disease, with good correlation with classical cardiovascular risk factors in the general population. The aim of this study was to evaluate the EFT in subclinical hypothyroidism (SCH), in comparison to a group without thyroid dysfunction. METHODS: A cross-sectional study was performed with 100 participants, including 52 SCH patients and 48 individuals without any thyroid dysfunction (euthyroid group-EU). Transthoracic echocardiography (TE), thyroid hormone levels, lipid profile, and assessment of body composition by bioelectrical impedance (BIA) and anthropometry were measured in all subjects. RESULTS: The SCH and EU groups were comparable with respect to age, gender, and Framingham risk scores. Serum thyroid-stimulating hormone (TSH) was 6.7 ± 1.4 mIU/L in the SCH group and 2.0 ± 0.84 mIU/L in the control group. EFT was similar in both groups (SCH 3.5 ± 1.3 mm, EU 3.5 ± 1.1 mm, p = 0.43). EFT showed a slight trend for a positive correlation with serum TSH in the SCH group (r s = 0.263, p = 0.05). EFT correlated with the body fat percentage in the SCH group (r s = 0.350, p = 0.03) and EU group (r s = 0.033, p = 0.04). EFT in this cohort was not independently correlated to changes in TSH and Framingham risk score. CONCLUSIONS: EFT determination by TE does not seem to be a good marker of cardiovascular risk in SCH patients with serum TSH <10.0 mIU/L and no pre-existing cardiovascular morbidity.

Effect of levothyroxine replacement on exercise performance in subclinical hypothyroidism.

Although muscle metabolism and exercise capacity seem to be affected in patients with subclinical hypothyroidism, there is little evidence indicating improvement of the exercise tolerance due to levothyroxine (L-T(4)) replacement. The aim of the present study was to verify possible cardiopulmonary changes during exercise in patients with subclinical hypothyroidism on L-T(4) replacement with a normal serum TSH for six months. Twenty-three patients with subclinical hypothyroidism were randomized into treated (no.=11) and untreated (no.=12) patients. A cardiopulmonary test was performed with a treadmill, using the modified Balke protocol. Heart rate, oxygen uptake, minute ventilation and other cardiopulmonary parameters were assessed at the 5th minute of exercise. FT4 levels increased while TSH normalized after hormone replacement. Oxygen uptake decreased significantly after hormone replacement (24.1+/-6.3 vs 17.1+/-4.2 ml x kg x min(-1); p=0.03).Minute ventilation also showed an enhanced performance in treated patients (28.0+/-8.1 vs 23.5+/-5.6 l x min(-1); p=0.03), as did the heart rate (128+/-17 vs 121+/-17 bpm; p=0.03). There were no changes in the untreated group. The results demonstrate that submaximal cardiopulmonary exercise performance improved after six months of TSH normalization and this improvement can help enhance the ability to carry out daily life activities in patients with subclinical hypothyroidism.

Effect of hormone replacement on exercise cardiopulmonary reserve and recovery performance in subclinical hypothyroidism.

Subclinical hypothyroidism (SH) patients present cardiopulmonary, vascular and muscle dysfunction, but there is no consensus about the benefits of levothyroxine (L-T4) intervention on cardiopulmonary performance during exercise. The aim of the present study was to investigate the effects of L-T4 on cardiopulmonary exercise reserve and recovery in SH patients. Twenty-three SH women, 44 (40-50) years old, were submitted to two ergospirometry tests, with an interval of 6 months of normalization of thyroid-stimulating hormone (TSH) levels (L-T4 replacement group) or simple observation (TSH = 6.90 µIU/mL; L-T4 = 1.02 ng/dL). Patients with TSH >10 µIU/mL were excluded from the study to assure that they would receive treatment in this later stage of SH. Twenty 30- to 57-year-old women with no thyroid dysfunction (TSH = 1.38 µIU/mL; L-T4 = 1.18 ng/dL) were also evaluated. At baseline, lower values of gas exchange ratio reserve (0.24 vs 0.30; P < 0.05) were found for SH patients. The treated group presented greater variation than the untreated group for pulmonary ventilation reserve (20.45 to 21.60 L/min; median variation = 5.2 vs 25.09 to 22.45 L/min; median variation = -4.75, respectively) and for gas exchange ratio reserve (0.19 to 0.27; median variation = 0.06 vs 0.28 to 0.18; median variation = -0.08, respectively). There were no relevant differences in cardiopulmonary recovery for either group at baseline or after follow-up. In the sample studied, L-T4 replacement improved exercise cardiopulmonary reserve, but no modification was found in recovery performance after exercise during this period of analysis.

Normal flow-mediated vasodilatation of the brachial artery and carotid artery intima-media thickness in subclinical hypothyroidism.

Subclinical hypothyroidism (SHT) is a disease for which exact therapeutic approaches have not yet been established. Previous studies have suggested an association between SHT and coronary heart disease. Whether this association is related to SHT-induced changes in serum lipid levels or to endothelial dysfunction is unclear. The aim of this study was to determine endothelial function measured by the flow-mediated vasodilatation of the brachial artery and the carotid artery intima-media thickness (IMT) in a group of women with SHT compared with euthyroid subjects. Triglycerides, total cholesterol, HDL-C, LDL-C, apoprotein A (apo A), apo B, and lipoprotein(a) were also determined. Twenty-one patients with SHT (mean age: 42.4 +/- 10.8 years and mean thyroid-stimulating hormone (TSH) levels: 8.2 +/- 2.7 microIU/mL) and 21 euthyroid controls matched for body mass index, age and atherosclerotic risk factors (mean age: 44.2 +/- 8.5 years and mean TSH levels: 1.4 +/- 0.6 microIU/mL) participated in the study. Lipid parameters (except HDL-C and apo A, which were lower) and IMT values were higher in the common carotid and carotid bifurcation of SHT patients with positive serum thyroid peroxidase antibodies (TPO-Ab) (0.62 +/- 0.2 and 0.62 +/- 0.16 mm for the common carotid and carotid bifurcation, respectively) when compared with the negative TPO-Ab group (0.55 +/- 0.24 and 0.58 +/- 0.13 mm, for common carotid and carotid bifurcation, respectively). The difference was not statistically significant. We conclude that minimal thyroid dysfunction had no adverse effects on endothelial function in the population studied. Further investigation is warranted to assess whether subclinical hypothyroidism, with and without TPO-Ab-positive serology, has any effect on endothelial function.

Treatment of subclinical hypothyroidism reduces atherogenic lipid levels in a placebo-controlled double-blind clinical trial.

Many studies have found clinical and metabolic alterations in subclinical hypothyroidism, however, there are disagreements about the benefits of levothyroxine therapy. The objective of the present study was to analyze the effects of 6 months of treatment on the lipid profile of patients with subclinical hypothyroidism. A randomized double blind, placebo-controlled clinical assay was conducted. Sixty patients were enrolled in stratified random allocation by TSH levels that generated similar groups in average: free thyroxine levels, lipid levels, age, clinical score, and sedentary. At 6 months, 18 patients in the levothyroxine and 20 in the placebo group were reevaluated and a fall in all atherogenic lipid variables was observed with treatment. The TC and LDL-c variations (-22.6+/-37.2 and -18.5+/-34.6 mg/dl, respectively) in the group that received LT4 were statistically different (p=0.023 and p=0.012) from those occurring in the placebo group (+7.3+/-37.1 and +14.7+/-40.6 mg/dl). Baseline characteristics associated with better improvement in the levels of TC and LDL-c were the presence of TPO-Ab, TSH levels >8.0 microUI/ml, Body Mass Index >or=25 kg/m2, and the presence of menopause. We concluded that treatment with dose-adjusted levothyroxine reduced atherogenic lipid levels in some patients. Further studies to determine the effects of LT4 replacement in specific subgroups of SH patients are still necessary, especially in patients with TSH <8.0 microUI/ml.

Effect of hormone replacement on exercise cardiopulmonary reserve and recovery performance in subclinical hypothyroidism

Subclinical hypothyroidism (SH) patients present cardiopulmonary, vascular and muscle dysfunction, but there is no consensus about the benefits of levothyroxine (L-T4) intervention on cardiopulmonary performance during exercise. The aim of the present study was to investigate the effects of L-T4 on cardiopulmonary exercise reserve and recovery in SH patients. Twenty-three SH women, 44 (40-50) years old, were submitted to two ergospirometry tests, with an interval of 6 months of normalization of thyroid-stimulating hormone (TSH) levels (L-T4 replacement group) or simple observation (TSH = 6.90 μIU/mL; L-T4 = 1.02 ng/dL). Patients with TSH >10 μIU/mL were excluded from the study to assure that they would receive treatment in this later stage of SH. Twenty 30- to 57-year-old women with no thyroid dysfunction (TSH = 1.38 μIU/mL; L-T4 = 1.18 ng/dL) were also evaluated. At baseline, lower values of gas exchange ratio reserve (0.24 vs 0.30; P < 0.05) were found for SH patients. The treated group presented greater variation than the untreated group for pulmonary ventilation reserve (20.45 to 21.60 L/min; median variation = 5.2 vs 25.09 to 22.45 L/min; median variation = -4.75, respectively) and for gas exchange ratio reserve (0.19 to 0.27; median variation = 0.06 vs 0.28 to 0.18; median variation = -0.08, respectively). There were no relevant differences in cardiopulmonary recovery for either group at baseline or after follow-up. In the sample studied, L-T4 replacement improved exercise cardiopulmonary reserve, but no modification was found in recovery performance after exercise during this period of analysis.

Normal flow-mediated vasodilatation of the brachial artery and carotid artery intima-media thickness in subclinical hypothyroidism

Subclinical hypothyroidism (SHT) is a disease for which exact therapeutic approaches have not yet been established. Previous studies have suggested an association between SHT and coronary heart disease. Whether this association is related to SHT-induced changes in serum lipid levels or to endothelial dysfunction is unclear. The aim of this study was to determine endothelial function measured by the flow-mediated vasodilatation of the brachial artery and the carotid artery intima-media thickness (IMT) in a group of women with SHT compared with euthyroid subjects. Triglycerides, total cholesterol, HDL-C, LDL-C, apoprotein A (apo A), apo B, and lipoprotein(a) were also determined. Twenty-one patients with SHT (mean age: 42.4 ± 10.8 years and mean thyroid-stimulating hormone (TSH) levels: 8.2 ± 2.7 µIU/mL) and 21 euthyroid controls matched for body mass index, age and atherosclerotic risk factors (mean age: 44.2 ± 8.5 years and mean TSH levels: 1.4 ± 0.6 µIU/mL) participated in the study. Lipid parameters (except HDL-C and apo A, which were lower) and IMT values were higher in the common carotid and carotid bifurcation of SHT patients with positive serum thyroid peroxidase antibodies (TPO-Ab) (0.62 ± 0.2 and 0.62 ± 0.16 mm for the common carotid and carotid bifurcation, respectively) when compared with the negative TPO-Ab group (0.55 ± 0.24 and 0.58 ± 0.13 mm, for common carotid and carotid bifurcation, respectively). The difference was not statistically significant. We conclude that minimal thyroid dysfunction had no adverse effects on endothelial function in the population studied. Further investigation is warranted to assess whether subclinical hypothyroidism, with and without TPO-Ab-positive serology, has any effect on endothelial function.