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

BACKGROUND: Previous 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.

METHODS: A 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).

RESULTS: Sub-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.

CONCLUSION: The 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.