“…Ten studies were marked as high risk of bias, six 41 , 42 , 43 , 44 , 45 , 46 of which failed to control for adequate confounding variables and four 47 , 48 , 49 , 50 which failed to sufficiently define their exposure variables. 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 Thirteen studies 14 , 17 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 were deemed to be of moderate risk of bias, with 16 studies deemed to be of low risk of bias 16 , 18 , 33 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 ( Fig. 2 ).…”