Tou-Yuan Tsai, Yu-Kang Tu, Kashif M Munir, Shu-Man Lin, Rachel Huai-En Chang, Sheng-Lun Kao, Ching-Hui Loh, Carol Chiung-Hui Peng, Huei-Kai Huang

The evidence of whether hypothyroidism increases mortality in the elderly population is currently inconsistent and conflicting. To determine the impact of hypothyroidism on mortality in the elderly population. PubMed, Embase, Cochrane Library, Scopus, and Web of Science databases from inception until May 10, 2019. Studies evaluating the association between hypothyroidism and all-cause and/or cardiovascular mortality in the elderly population (aged ≥ 60 years) were eligible. Two reviewers independently extracted data and assessed the quality of studies. The relative risk (RR) was retrieved for synthesis. Random-effects model for meta-analyses was used. A total of 27 cohort studies with 1,114,638 participants met the inclusion criteria. Overall, patients with hypothyroidism experienced a higher risk of all-cause mortality than those with euthyroidism (pooled RR=1.26, 95% CI: 1.15-1.37); meanwhile, no significant difference in cardiovascular mortality was found between patients with hypothyroidism and those with euthyroidism (pooled RR=1.10, 95% CI: 0.84-1.43). Subgroup analyses revealed that overt hypothyroidism (pooled RR=1.10, 95% CI: 1.01-1.20) rather than subclinical hypothyroidism (pooled RR=1.14, 95% CI: 0.92-1.41) was associated with increased all-cause mortality. The heterogeneity primarily originated from different study designs (prospective and retrospective) and geographic locations (Europe, North America, Asia, and Oceania). Based on the current evidence, hypothyroidism is significantly associated with increased all-cause mortality instead of cardiovascular mortality among the elderly. We observed considerable heterogeneity, so caution is needed when interpreting the results. Further prospective large-scale high-quality studies are warranted to confirm these findings.