title: Association between circulating irisin and insulin resistance in non-diabetic adults: A meta-analysis.
abstract: BACKGROUND
  Exogenous administration of recombinant irisin improves glucose metabolism. However, the association of endogenous circulating (plasma/serum) irisin with insulin resistance remains poorly delineated. This study was aimed to examine this association by meta-analyzing the current evidence without study design restriction in non-diabetic adults.
  
  
  METHODS
  Peer-reviewed studies written in English from 3 databases were searched to December 2015. Studies that reported the association between circulating irisin and insulin resistance (or its reverse, insulin sensitivity) in non-diabetic non-pregnant adults (mean ages ≥18years) were included. The pooled correlation coefficient (r) and 95% confidence intervals (CIs) were calculated using a random-effects model. Subgroup analyses and meta-regression were performed to explore potential sources of heterogeneity.
  
  
  RESULTS
  Of the 195 identified publications, 17 studies from 15 articles enrolling 1912 participants reported the association between circulating irisin and insulin resistance. The pooled effect size was 0.15 (95% CI: 0.07 to 0.22) with a substantial heterogeneity (I(2)=55.5%). This association seemed to be modified by glycemic status (fasting blood glucose ≥6.1mmol/L versus <6.1mmol/L) and racial-ethnic difference (Asians versus Europeans versus Americans), but not by sex difference, sampling time-point, blood sample type, ELISA kits used, baseline age, or body mass index. Circulating irisin was inversely associated with insulin sensitivity (6 studies; r=-0.17, 95% CI: -0.25 to -0.09).
  
  
  CONCLUSIONS
  Circulating irisin is directly and positively associated with insulin resistance in non-diabetic adults. However, this association is rather small and requires further clarification, in particular by well-designed large epidemiological studies with overall, race-, and sex-specific analyses.
authors.affiliation: Department of Endocrinology, Zhongda Hospital, Institute of Diabetes, School of Medicine, Southeast University, Nanjing, P.R. China.
authors.forename: Shanhu
authors.initials: S
authors.lastname: Qiu
authors.affiliation: Department of Endocrinology, Zhongda Hospital, Institute of Diabetes, School of Medicine, Southeast University, Nanjing, P.R. China.
authors.forename: Xue
authors.initials: X
authors.lastname: Cai
authors.affiliation: Department of Endocrinology, Zhongda Hospital, Institute of Diabetes, School of Medicine, Southeast University, Nanjing, P.R. China; Division of Sports and Rehabilitation Medicine, Department of Internal Medicine II, Ulm University, Ulm, Germany.
authors.forename: Han
authors.initials: H
authors.lastname: Yin
authors.affiliation: Division of Sports and Rehabilitation Medicine, Department of Internal Medicine II, Ulm University, Ulm, Germany.
authors.forename: Martina
authors.initials: M
authors.lastname: Zügel
authors.affiliation: Department of Endocrinology, Zhongda Hospital, Institute of Diabetes, School of Medicine, Southeast University, Nanjing, P.R. China. Electronic address: sunzilin1963@126.com.
authors.forename: Zilin
authors.initials: Z
authors.lastname: Sun
authors.affiliation: Division of Sports and Rehabilitation Medicine, Department of Internal Medicine II, Ulm University, Ulm, Germany.
authors.forename: Jürgen Michael
authors.initials: JM
authors.lastname: Steinacker
authors.affiliation: Division of Sports and Rehabilitation Medicine, Department of Internal Medicine II, Ulm University, Ulm, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Schumann
mesh_terms: D000328:Adult; D005353:Fibronectins / Q000097:blood*; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*
chemical_list: C577593:FNDC5 protein, human; D005353:Fibronectins
keywords: Insulin resistance; Irisin; Meta-analysis