Nonalcoholic Fatty Liver Disease Is Not Associated with Thyroid Hormone Levels and Hypothyroidism: A Systematic Review and Meta-Analysis
Background: Whether hypothyroidism is related to nonalcoholic fatty liver disease (NAFLD) is unclear. Thyroid dysfunction is closely related with components of metabolic syndrome. Given the hepatic manifestation of metabolic syndrome, several studies have investigated the association between NAFLD and thyroid dysfunction and have demonstrated inconsistent results. Thus, we conducted a systematic review and meta-analysis to better characterize the association between NAFLD and thyroid dysfunction. Methods: MEDLINE and Embase were searched through July 2016. The primary outcome was the association between NAFLD and subclinical, overt, and overall hypothyroidism. The secondary outcome was the difference in thyroid hormone levels (free triiodothyronine [FT3], free thyroxine [FT4], or thyroid-stimulating hormone [TSH]) between NAFLD patients and non-NAFLD controls. Pooled odds ratios (OR) and 95% CI were calculated using a random-effects model. All continuous data are summarized as the mean difference along with 95% CI. Results: Data were extracted from 14 studies involving 7,191 NAFLD patients and 30,003 controls. NAFLD was not associated with subclinical, overt, or overall hypothyroidism compared with non-NAFLD controls. Patients who had NAFLD did not show a significant difference in FT3, FT4, or TSH compared with non-NAFLD controls. Conclusions: Our meta-analysis demonstrates no significant association between NAFLD and subclinical, overt, or overall hypothyroidism, and we also found no significant difference in thyroid hormone levels between participants with and without NAFLD.