Reply to: Meta-analysis of vitamin D supplementation and hemoglobin concentration: methodological faults obscure the interpretation of the data.

Dear Editor,

We would like to thank Mr. Raeisi-Dehkordi, et al. [1] for their interest and knowledgeable comments on our study.

We have followed the PRISMA guidelines according to the most recent research standards (page 3 of the article). PICOS was also used in the study design (amendments are made on page 2). While it is not compulsory to submit all systematic reviews at PROSPERO, all the principles mentioned in PROSPERO were followed. In the corrected version of the paper [2], we have clarified that no restrictions were placed on the gender, race, and geographical distribution of the individuals enrolled in the study. However, age restrictions were places such that the studies carried out in subjects with a mean age of ≥17.5 years old were included. Also, the type of supplementation has been corrected to include all types of vitamin D supplementation and not just oral vitamin D supplementation. According to the Cochrane handbook, including multiple comparisons from one study with a shared intervention group to the meta-analysis may lead to bias [3]. However, in many published articles this method has been used. Therefore, we decided to use this method based on previous research [4, 5]. According to your suggestion, the stated combination of supplementary studies [6, 7] were removed from the final analysis and a new Forrest plot was introduced. However, no changes in the results were observed (Figs. 2, 3, 4 and 5).

Fig. 2

Forest plot showing results of a meta-analysis on the effects of vitamin D supplementation on hemoglobin. Data were reported as SMDs with 95% CIs

Fig. 3

Forest plot showing results of a meta-analysis on the effects of vitamin D supplementation on ferritin. Data were reported as SMDs with 95% CIs

Fig. 4

Forest plot showing results of a meta-analysis on the effects of vitamin D supplementation on transferrin saturation. Data were reported as MDs with 95% CIs

Fig. 5

Forest plot showing results of a meta-analysis on the effects of vitamin D supplementation on iron levels. Data were reported as SMDs with 95% CIs