I would keep in mind that this paper is a meta analysis. There is a HUGE caveat to meta analyses (you can wiki these), of which the biggest issue is researcher agenda/bias. Depending on their inclusion criteria (and also taking into account the effect where studies with "no effect" tend to not be published), this can sway the outcome. People doing these meta analyses already have an opinion and if they look for it, they will get the result they want if they are not honest or strict with what they include. The fact that they only looked through PubMed and Google Scholar for their meta analysis is already a HUGE red flag that there are a ton of other studies they are ignoring because they were too lazy to look up everything out there.