Serum total antioxidant status and lipid peroxidation marker malondialdehyde levels in overt and subclinical hypothyroidism

Mitochondria are the main production site of free oxygen radicals, which can cause organ dysfunction by oxidation of cellular macromolecules such as carbohydrates, lipids and proteins. Oxidative stress may result from either overproduction of these species or from failure of the antioxidant defence systems. Thyroid hormones have well-known effects on mitochondrial oxygen consumption, but data about how hypothyroidism affects oxidative stress are controversial, and little is known about oxidative stress in subclinical hypothyroidism. Total antioxidant status (TAS) gives information about all of the antioxidants in the organism, while malondialdehyde (MDA) is a lipid peroxidation marker used to assess lipid peroxidation due to increased oxidative stress. We aimed to determine how hypothyroidism and subclinical hypothyroidism affect serum MDA and TAS. Serum TAS, MDA, C-reactive protein levels and lipid compositions were studied in 20 hypothyroid, 40 subclinical hypothyroid and 40 healthy subjects. MDA was elevated in both hypothyroid and subclinical hypothyroid patients compared with controls, while TAS levels show no significant differences between groups. Low-density lipoprotein (LDL) cholesterol levels were significantly high in both hypothyroid and subclinical hypothyroid patients. Triglyceride levels were high only in hypothyroid patients when compared with the controls. MDA showed a correlation with LDL cholesterol, total cholesterol and triglyceride. These results suggest an increased oxidative stress in both hypothyroid and subclinical hypothyroidism states, which can be explained by both the insufficient increase in the antioxidant status and the altered lipid metabolism in these cases.