Combined vitamin C and E supplementation for preeclampsia: no significant effect but significant heterogeneity?

it is very likely to be a case control rather than a randomized controlled trial. Considering that results from observational studies are not high-quality evidence and are prone to biases, mainly because of the failure to adjust for potential confounding factors, possibly in this trial the effect of vitamin supplementation on the incidence of preeclampsia may be flawed. Finally, a feasible explanation may be a local literature bias, known as a “reverse tower of Babel bias,” which has been previously reported (7). In certain cases locally produced and published literature is spuriously statistically significant (7,8), and this may be the case with these two trials. In conclusion, sources of bias must always be indentified in meta-analyses and statistical heterogeneity must be interpreted with caution. Nikolaos P. Polyzos, Spyridon Tzioras, Davide Mauri Panhellenic Association for Continual Medical Research (PACMeR), Sections of Obstetrics and Gynaecology and Public Health,