Thyroid hormone therapy for obesity and nonthyroidal illnesses: a systematic review.

CONTEXT: Thyroid hormone therapy to enhance weight loss in obesity during caloric deprivation and 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 T(4) therapy in these populations. DATA SOURCES: Electronic databases and reference lists were searched. STUDY SELECTION: Studies with comparable control groups comparing T(3) and/or T(4) 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, T(3) therapy decreased serum TSH and T(4) concentrations. Consistent effects of T(3) or T(4) on weight loss, protein breakdown, metabolic rate, and heart rate could not be established. In euthyroid cardiac patients, T(3) decreased TSH and free T(4) levels, without consistent effects of T(3) or T(4) on heart rate, cardiac output, or systemic vascular resistance. Mortality increased 3.3-fold with T(4) therapy in acute renal failure patients, whereas 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.