Effect of tyroxine therapy on postprandial lipid-cholesterol and glucose levels in subclinical hypothyroidism

Although an increase of cardiovascular disease risk in patients with subclinical hypothyroidism is showed by clinical trials, the underlying mechanism is not well understood yet. The controversy of whether there is an atherogenic lipidcholesterol change in patients with subclinical hypothyroidism and whether it is recovered by tyroxine treatment suggested presence of different mechanism in pathogenesis. It is known that some metabolic events in postprandial phase cause endothelial damage and that is contribute to atherosclerosis development. Until now, there was no clinical trial about metabolic changes in postprandial phase in patients with subclinical hypothyroidism. The aim of this study is to investigate whether there is an atherogenic lipid-cholesterol parameters in fasting and postprandial phase in patients with subclinical hypothyroidism and whether tyroxine therapy have an effect on fasting and postprandial lipid-cholesterol levels in patients with subclinical hypothyroidism. Fifty subclinical hypothyroid and 25 euthyroid patients enrolled to study. First 25 subclinical hypothyroid patients consist treatment group (group I), second 25 subclinical hypothyroid patients consist control group (group II) and 25 euthyroid patient consist euthyroid control group (group III). All of patients had a standard testing meal consisting of 32 g protein, 76.6 g carbohydrate, 21.5 g lipid and totally 650 kilocalories. Before and after 2 hour from meal, blood samples for glucose, insulin, triglyceride, HDL cholesterol, total cholesterol, LDL cholesterol was taken. After that, the patients in subclinical hypothyroid treatment group (group I) started to take levothyroxine 50 μg daily. The patients in subclinical hypothyroid control group (group II) did not take any drug. Patients continued to preexisting feeding behaviour. Three months later, for two group (group I and group II) blood samples were taken with same procedure in the beginning. Fasting and postprandial glucose levels were lower in subclinical hypothyroid patients than euthyroid patients (p=0.02 ve p=0.00), but according to serum insulin and lipid-cholesterol levels there was no difference between subclinical hypothyroid patients and euthyroid patients. Although there was no difference between subclinical hypothyroid treatment group (group I) and subclinical hypothyroid control group (group II) in the beginning, fasting and postprandial cholesterol levels were lower in subclinical hypothyroid treatment group (group I) at the end of three months (p=0.01 ve p=0.00). But, there was no difference between two groups according to fasting and postprandial LDL cholesterol and triglyceride levels. In treatment group, we found a decrease in postprandial glucose level with levothyroxine therapy at the end of study, although there was no change in fasting and postprandial insulin and fasting glucose levels. In the beginning in the patients with subclinical hypothyroidism and at the end of three months in the treatment group there was no correlation between thyroid hormone levels and basal and postprandial glucose, insulin, total cholesterol, LDL cholesterol, HDL cholesterol, triglyceride level changes. Also, in the beginning in the patients with subclinical hypothyroidism and at the end of three month in the treatment group there was no correlation between thyroid hormone levels and basal and postprandial glucose, insulin, total cholesterol, LDL cholesterol, HDL cholesterol, triglyceride levels. Eventually, in our study, in fasting and in postprandial state there was no findings of atherogenic lipid-cholesterol and glucose profile in subclinical hypothyroid patients with mild TSH elevation. In addition, except postprandial glucose there was no changes in atherogenic lipid-cholesterol and fasting glucose levels with levothyroxine treatment in subclinical hypothyroid patients. Key words: Subclinical hypothyroidism, fasting and postprandial phase, lipidcholesterol profile, thyroxine therapy