Serum Biomarkers for Cardiovascular Inflammation in Subclinical Hypothyroidism

Objective: Cardiovascular disease has been reported to be more common in patients with elevated levels of TSH and with normal thyroxine levels, termed subclinical hypothyroidism (SCH). The aim of this study was to determine whether individuals with SCH were more likely than euthyroid controls to have elevations in inflammatory biomarkers that are associated with cardiac disease.

Methods: From the National Health and Nutrition Examination Survey (NHANES) 1999-2002 data we identified respondents aged > or = 40 who met the laboratory criteria for SCH. We compared the average values and frequencies of elevated C-reactive protein (CRP) and homocysteine in the SCH individuals to those in euthyroid individuals. Results A total of 1608 individuals were included in the analysis of whom 45 (2.8%) met the criteria for SCH, with seven (15.6%) having TSH levels between 10 and 15 IU/l. We found no differences in median, mean or the percentage of elevated CRP or homocysteine in individuals with SCH compared to euthyroid controls. Linear regression models adjusting for age, gender, the presence of other cardiac risk factors, and whether the individual was using a cholesterol-lowering drug also failed to show any association between SCH and either high-sensitivity CRP (hsCRP) (P = 0.62) or homocysteine (P = 0.63) levels. When we examined the subset of people with TSH levels between 10 and 15 IU/l, we again found no difference in mean hsCRP or homocysteine compared to control.

Conclusions: In this large population-based sample, hsCRP and homocysteine levels do not differ for individuals with SCH compared to euthyroid individuals. This suggests that cardiac inflammation is not greater in individuals with SCH.