Introduction In subclinical hypothyroidism (SH), serum lipid and lipoprotein concentrations are frequently changed. Compared with the healthy population, the levels of oxidized low-density lipoprotein cholesterol are higher, and the levels of high-density lipoprotein cholesterol are lower. In patients with SH, the mechanism of atherosclerosis may beattributed to the lipid abnormalities. There is evidence showing that oxidation plays an important role during the process of atherosclerosis. Inthis study, we evaluated the activity of paraoxonase (PON) and arylesterase (ARE) in patients with SH and investigated their relation with oxidative stress.

Results Between 2 groups, no significant difference was found in terms of age, sex, serum levels of total cholesterol, low-density lipoprotein, and high-density lipoprotein. In the SH group, the activity of PON was significantly lower than that observed in the control group (P < 0.05). Arylesterase activity also was significantly lower in the group with SH, compared with the control group (P < 0.05). Oxidative stress index was found to be significantly higher in the patient group, compared with the healthy subjects (P < 0.01). Oxidative stress index showed a strong positive correlation with the levels of thyroid stimulating hormone in all cases (r = 0.60, P < 0.01).

Conclusions The activity of PON and ARE were significantly decreased, and oxidative stress was increased in patients with SH. Lower activities of these 2 biomarkers indicate increased oxidative damage in SH. Atherosclerosis in SH can be attributed to increased oxidative stress.