Association of Hypothyroidism and Mortality in the Elderly Population: A Systematic Review and Meta-Analysis

Context: The evidence of whether hypothyroidism increases mortality in the elderly population is currently inconsistent and conflicting. Objective: The objective of this meta-analysis is to determine the impact of hypothyroidism on mortality in the elderly population. Data Sources: PubMed, Embase, Cochrane Library, Scopus, and Web of Science databases were searched from inception until May 10, 2019. Study Selection: Studies evaluating the association between hypothyroidism and all-cause and/or cardiovascular mortality in the elderly population (ages >= 60 years) were eligible. Data Extraction: Two reviewers independently extracted data and assessed the quality of the studies. Relative risk (RR) was retrieved for synthesis. A random-effects model for meta-analyses was used. Data Synthesis: 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). Conclusions: 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.