“…However, a wide heterogeneity was observed which made it impossible to perform an advanced statistical analysis. Eight studies were case–control [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ], two were cohort studies [ 35 , 36 ], and one was a cross-sectional cohort study [ 37 ]. Of the eleven studies, five were from Taiwan [ 30 , 34 , 35 , 36 , 37 ], three were from China [ 28 , 29 , 32 ], one was from the USA [ 27 ], one was from Sudan [ 31 ], and one was from Japan [ 33 ].…”