This isn't a conclusion based simply on some cohort or case-control studies. There are many, many randomized controlled trials.

这一结论不只是基于一些世代研究或病例对照研究，而是基于无数随机对照试验。

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Of the available studies, 29 were cohort studies, 69 case-control studies, and 4 randomized clinical trials.

现有的研究包括29个队列研究，69个病例对照研究以及4个随机临床试验。

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