Double-counting of effect sizes and inappropriate exclusion of studies in "The influence of vitamin D supplementation on IGF-1 levels in humans: A systematic review and meta-analysis".

We read with interest the review by Kord-Varkaneh et al. which examined the effects of vitamin D supplementation on IGF-1 levels in humans. We believe that the article suffers from severe methodological faults and subsequently the conclusions are likely to be biased. Thus, the authors should address the mentioned limitations and update the analyses to provide robust and trustful estimates. We are concerned that without correction, the analyses may lead to erroneous findings and conclusions.