“…Five of the eligible studies were a cohort design [15,20,21,23,36], one was a case–control design [37] and the remaining 19 studies were cross-sectional [7,8,19,22,24-34,38-41]. The majority of studies were published from 2009 onwards (n = 22, 84.6%), with precise publication years being; 2002 [26], 2007 [30], 2008 [25], 2009 [19,21,22,24,28,29,32,36-38], 2010 [7,33,34] and 2011 [8,15,20,23,27,31,39-41]. Eleven studies were undertaken in United States of America (USA) [19,26,29,31-34,39-42], three were conducted in Japan [22,23,27], two were undertaken in Spain [20,36].…”