“…No study had low risk of bias for all domains ( Table 2). Only seven studies adjusted for potential confounding (19,39,40,50,52,54,59) and nine studies were at high risk of bias due to possible confounding (20,38,43,(45)(46)(47)(48)53,60) . Seven studies had high risk of bias relating to ascertainment of exposures (38,39,42,47,48,50,59) because exposures were not measured prior to outcomes of interest or were not well defined (38,47,48,59) .…”