Endothelial dysfunction and low grade chronic inflammation in subclinical hypothyroidism due to autoimmune thyroiditis.

The relationship between subclinical hypothyroidism (SH) and cardiovascular disease has been one of the most popular topics recently. There is still some controversy concerning its cardiovascular impact and management protocols. Our study aims to investigate the presence of the well known preceding clinical situations of atherosclerosis like endothelial dysfunction and inflammation in subclinical hypothyroidism. Thirty-seven patients with subclinical hypothyroidism (29 women, 8 men) and 23 healthy volunteers (19 women, 4 men) were recruited for the study. Endothelial dysfunction was measured by examining brachial artery responses to endothelium-dependent (flow mediated dilation, FMD) and endothelium-independent stimuli (sublingual nitroglycerin (NTG)). Serum TNF-alpha, interleukin-6, and hs-CRP were measured. The estimate of insulin resistance by HOMA score was calculated with the formula: fasting serum insulin (µIU/mL) x fasting plasma glucose (µM/L) / 22.5. There were no significant differences in age, body mass index, waist circumference, HOMA scores. There was a statistically significant difference in endothelium-dependent (FMD) and endothelium-independent vascular responses (NTG) between the patients with subclinical hypothyroidism and the normal healthy controls. The groups were well matched for baseline brachial artery diameter. The TSH and LDL, IL-6, TNF-alpha and hs-CRP levels in the patient group were significantly higher than those in control group. A positive correlation was found only between endothelium-dependent vasodilation and TNF-alpha, hs-CRP and IL-6, TSH, total cholesterol, LDL and triglycerides. Endothelium-independent vascular response was not correlated with any of the metabolic or hormonal parameters. Neither of the groups were insulin resistant and there was not any difference either in fasting insulin or in glucose levels. We found endothelial dysfunction in subclinical hypothyroidism group. Endothelium-dependent (FMD) and endothelium-independent vascular responses (NTG) were lower in patient group. Our findings suggest that there is endothelial dysfunction and low grade chronic inflammation in SH due to autoimmune thyroiditis. There are several contributing factors which can cause endothelial dysfunction in SH such as changes in lipid profile, hyperhomocysteinemia. According to our results low grade chronic inflammation may be one of these factors.