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Findings of a Relation Between Vitamin D and C-Reactive Protein: Concerns About Methods Used and Conclusions Drawn

The epidemiologic study suggesting a relation between serum 25-hydroxyvitamin D (25[OH]D) and C-reactive protein (CRP) by Amer and Qayyum 1 is timely, given the prominence of 25(OH)D in recent scientific research and the recent increase in vitamin D recommended daily allowances. 2 However, the study appears to suffer from deficiencies in internal validity (due to the analysis methods used) and external validity (because vitamin D supplementation by subjects was not included in the analysis). Their findings contradict evidence for a dose-dependent reduction of coronary heart disease mortality with higher serum 25(OH)D, 3 and furthermore, CRP has questionable utility in guiding treatment of patients with coronary heart disease. 4 Best practices in data analysis suggest several steps that should have been taken to avoid bias and uncertainty. The scale of the y axis in Figure 1 should have been back-transformed from the logarithm of CRP to its raw (original) value. The investigators' multivariate analysis results are counterintuitive, because in Table 1, we can read that subjects with 25(OH)D levels <21 ng/ml had higher mean CRP levels than subjects with 25(OH)D levels >21 ng/ml. An appropriately scaled graph would allow readers to visually grasp the relations being examined and assess http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The American Journal of Cardiology Elsevier
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