Subclinical (hypothyroidism, SCH and hyperthyroidism, SH) thyroid disorders are common, but their clinical management remains controversial. Both SCH and SH may be associated with increased cardiovascular risk (CVR); SCH being associated with atherogenic lipid profile, endothelial dysfunction assessed by brachial artery flow mediated dilatation (FMD) and some evidence for cardiovascular disease, whereas SH has been associated with atrial fibrillation. Endothelial progenitor cells (EPCs) has been shown to be a novel CVR factor. Reduced number and or function of EPCs have been associated with cardiovascular risk factors and disease. Methods: We have studied circulating endothelial progenitor cells (CEPC) in peripheral blood, endothelial cell like cells (EC like cells) after culture along with FMD, lipid profile and asymmetric dimethyl arginine (ADMA) in 20 SCH, SH, 11 hypothyroid (HT) in comparison to 20 control subjects. Results: CEPC numbers m peripheral blood (CD34+NEGFR-2+, CD 133+NEGFR-2+, CD 144+/CD34+ and CD 144+/CD 133+) were significantly reduced in SCH, HT and SH compared to controls. Both SCH and SH predicted lower CEPC numbers after adjusting for CVR factors in regression analysis. Furthermore, CEPCs improved after thyroxine replacement in SCH and HT. EC like cell number after culture was lower in HT, but no difference in SCH and SH compared to controls. There was no difference in the functions of EC like cells in all groups. Serum high density lipoprotein cholesterol was lower in SCH and hypothyroid subjects, whereas FMD was lower in 9 SH subjects compared to controls. Conclusion: Our finding further supports the concept that both SCH and SH are not just a biochemical abnormality and lower CEPC numbers may contribute to increased CVR in those disorders. Further research is vital to explore the mechanisms behind this finding and also to evaluate treatment strategies in both SCH and SH is translated into an improvement in cardiovascular outcome.

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