Impact of subclinical thyroid disorders on coronary heart disease, cardiovascular and all-cause mortality: A meta-analysis

BackgroundPrevious studies have suggested that sub-clinical thyroid states may have detrimental effects on the coronary heart disease (CHD). Whether subclinical thyroid dysfunction is a risk factor for the above is controversial.MethodsA systemic search of the literature using Pubmed, Medline and Ovid online tool was performed to identify relevant studies. Amongst the clinical studies, crossectional study and studies with follow-up period ranging between 4 and 20 yr were identified (Walsh JP, Bremner AP, Bulsara MK, et al. Subclinical thyroid dysfunction as a risk factor for cardiovascular disease. Arch Intern Med 2005 Nov 28;165 (21):2467–72.; Rodondi N, Newman AB, Vittinghoff E, et al. Subclinical hypothyroidism and the risk of heart failure, other cardiovascular events, and death. Arch Intern Med 2005 Nov 28; 165 (21):2460–6.; Rotterdam study, Imaizumi M, Akahoshi M, Ichimaru S, et al. Risk for coronary heart disease and all-cause mortality in subclinical hypothyroidism. J Clin Endocrinol Metab 2004 Jul; 89 (7):3365–70.; Capolla et al.; Parle JV, Maisonneuve P, Sheppard MC, Boyle P, Franklyn JA. Prediction of all-cause and cardiovascular mortality in elderly people from one low serum thyrotropin result: a 10-year cohort study. Lancet 2001 Sep 15; 358 (9285):861–5).ResultsSub-clinical hypothyroidism: The pooled estimate of the relative risk of CHD revealed significant difference both at baseline [RR with 95% CI: 1.533 (1.312–1.791), P < 0.05] and at follow-up [RR with 95% CI: 1.188 (1.024–1.379), P < 0.05]. The relative risk of all-cause mortality at follow-up revealed no significant difference. However, the relative risk of death from cardiovascular causes at follow-up was significantly higher [RR with 95% CI: 1.278 (1.023–1.597), P < 0.05]. Sub-clinical hyperthyroidism: The pooled estimate of the relative risk of CHD revealed no significant difference both at baseline [RR with 95% CI: 1.156 (0.709–1.883)] and at follow-up [RR with 95% CI: 1.207 (0.780–1.870)].The relative risk of death from cardiovascular causes at follow-up was also not significantly higher.ConclusionThe present meta-analysis indicates that sub-clinical hypothyroidism is associated with both, a significant risk of CHD at baseline and at follow-up. In addition, mortality from cardiovascular causes is significantly higher at follow-up. Sub-clinical hyperthyroidism is not associated with CHD or mortality from cardiovascular causes.