Twenty-five observational studies (14 cohort and 11 case control studies) that measured blood or toenail selenium concentrations and 6 randomized trials that evaluated supplements containing selenium met our inclusion criteria.

• 结果：有25个检测血或趾甲中硒浓度的观察性研究（14个群体研究和11个病例对照研究）和6个评价含硒补充剂的随机试验符合我们的选择标准。