As with most meta-analyses, our study also had some limitations. First, we may have failed to control for potential confounders. Although most studies controlled for some lifestyle factors, it is difficult to completely eliminate the residual confounding factors. Second, recall bias may have been present in original studies when food-frequency and recall questionnaires were used to assess diet. This would have inevitably led to some degree of misclassification of folate intake (Larsson et al., 2006). Third, publication bias may be present because of language restrictions. In the subgroup analyses based on area, design, outcome of cases, NOQAS score, and five adjusted confounders, we observed an inverse association between folate intake and the risk of EC in almost all groups, but not in the cohort study design (OR=1.01, 95% CI: 0.79–1.30) and in the group with a NOQAS score of 6 (OR=0.96, 95% CI: 0.59–1.57). Only two cohort studies exist to date. The limited data from cohort studies might lead to bias in this subgroup result.
All work was completed at Shandong University, China. I thank my study team during the writing of this thesis for their support.
There are no conflicts of interest.
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