Abstract
Both thyroid hormones and irisin have profound influences on the metabolism of the human body. Based on their similarities, several studies have been conducted to explore changes in irisin levels in patients with hypothyroidism and hyperthyroidism. This study was conducted in accordance with the PRISMA statement and the MOOSE reporting guideline. Based on a preregistered protocol (PROSPERO—CRD42019138430), a comprehensive search of eight databases was performed from inception to April 2020. Studies with original data collected from patients with thyroid dysfunction were included. Subgroup analysis was performed based on the different types of clinical manifestations and patient characteristics. The quality of each study and the presence of publication bias were assessed by the Newcastle-Ottawa score (NOS) and funnel plot with Egger's test, respectively. A total of 11 studies with 1210 participants were included. Ten studies were identified as high-quality studies. Pooled analysis indicated decreased irisin levels in patients with hypothyroidism (MD -10.37, 95% CI -17.81 to -2.93). Subgroup analysis revealed an even lower level of irisin in patients with clinical-type hypothyroidism (MD -17.03, 95% CI -30.58 to -3.49) and hypothyroidism caused by autoimmune disease (MD -19.38, 95% CI -36.50 to -2.26). No differences were found after achieving euthyroid status from levothyroxine treatment in patients with hypothyroidism compared with controls. No differences were found between patients with hyperthyroidism and controls. Correlation analyses revealed a possible negative correlation between irisin and TSH and positive correlations between irisin and both fT3 and fT4. Irisin was correlated with TSH receptor antibodies.
Highlights
Thyroid hormones have profound influences on the metabolic status of the human body; they can regulate both obligatory and facultative thermogenesis and have considerable effects on the cardiovascular system [1, 2]
Irisin is involved in the expression of peroxisome proliferator-activated receptor- (PPAR-) gamma and uncoupling protein- (UCP-) 1, which are the hallmarks of thermogenesis [14]
Five studies were based in Turkey [28,29,30,31,32], three studies were based in Poland [33,34,35], two studies were based in Greece [36, 37], and one study was based in China [38]
Summary
Thyroid hormones have profound influences on the metabolic status of the human body; they can regulate both obligatory and facultative thermogenesis and have considerable effects on the cardiovascular system [1, 2]. Both hyperthyroidism and hypothyroidism are common, and the prevalence of hyperthyroidism is approximately 0.8% in Europe, 1.3% in the USA, and 1.1% in China [3,4,5,6]. Animal studies have shown that the hypothalamic-pituitary-thyroid (HPT) axis function may be directly or indirectly related to irisin modulation, or vice versa [17,18,19]
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