The associations between serum 25-hydroxyvitamin D and red blood cell indices reported from the KiGGS study are, except for mean corpuscular hemoglobin, not mediated by health-related quality of life

Excerpt

In the April 2018 issue of the European Journal of Pediatrics, we published results from the nationwide and representative KiGGS study in German adolescents aged 11 to 17 years, showing significant associations between serum 25-hydroxyvitamin D (25[OH]D) concentrations and clinically important hematological markers of red blood cells [2]. In a letter to the editor, Virella and colleagues expressed concerns regarding the statistical methodology used in our paper [4]. We appreciate their well-advised comment on our paper and, indeed, completely agree with their criticism that the proportion of published false-positive findings is expected to increase with decreasing effect sizes, as was reported in our article. Unfortunately, however, Virella et al. did not consider in their comment that there is likewise an increased probability that statistically significant results may, in fact, be false-positive when a study is underpowered due to an unacceptably low sample size [1 ]. In view of the large sample size of the KiGGS cohort, we have clearly acknowledged this methodological limitation in the “Discussion” section of our original paper and, in addition, pointed out that due to the cross-sectional analysis, any causal interpretation of our findings is not allowed. Given the sample heterogeneity and the overall small range of hematological measurements, it is not surprising that the reported effect sizes in our analysis were generally small. …