Thyroid hormone therapy for obesity and nonthyroidal illnesses: A systematic review

Abstract

Context: Thyroidhormonetherapy toenhanceweight loss in obesity during caloric deprivationand to improve morbidity and mortality in adults with nonthyroidal illnesses remains controversial. Objective: The aim of this study was to conduct a systematic review evaluating effectiveness and risks of T 3 and/or T4 therapy in these populations. Data Sources: Electronic databases and reference lists were searched. Study Selection: Studies with comparable control groups comparing T3 and/or T4 therapy to placebo in randomized controlled trials (RCTs) or prospective observational studies were selected. Data Extraction: Three reviewers performed serial abstraction. Data Synthesis: During caloric deprivation of obese subjects, T3 therapy decreased serum TSH and T4 concentrations. Consistent effects of T3 or T4 on weight loss, protein breakdown, metabolic rate, and heart rate could not be established. In euthyroid cardiac patients, T3 decreased TSH and free T4 levels, without consistent effects of T3 or T 4 on heart rate, cardiac output, or systemic vascular resistance. Mortality increased 3.3-fold with T4 therapy in acute renal failure patients, where as an effect in cardiac, critically ill, and burn patients could not be established. Equivalence testing indicated that larger RCTs are required to determine whether thyroid hormone therapy alters end-points in obesity or nonthyroidal illnesses. Limitations: Numbers of usable unique studies were small, numbers of patients in each study were inadequate, end-points were variable, few RCTs were performed, and study quality of non-RCTs was poor. Conclusions: Available data are inconclusive regarding effectiveness of thyroid hormone therapy in treating obesity or nonthyroidal illnesses, whereas data support that such therapy induces subclinical hyperthyroidism. Copyright © 2009 by The Endocrine Society.