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. 2020 Jun 3;19:52. doi: 10.1186/s12937-020-00556-6

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© The Author(s) 2020

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

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Fig. 1 — Flow chart of study selection. A flowchart of the research selection process of this meta-analysis is shown in Fig. 1. The search of database and other sources identified 1679 potentially relevant articles after duplicate exclusion. In addition, 1645 articles were excluded after further evaluations. Finally, 34 articles reporting 35 studies were selected for this meta-analysis