Simpsonʹs Paradox and the Association Between Vitamin D Deficiency and Increased Heart Disease

Several recent investigations have highlighted a potential link between vitamin D deficiency and increased heart disease. Observational studies suggest cardioprotective benefits related to supplementation, but randomized trials remain to be conducted. This report adds a caution based on a statistical paradox that is rarely mentioned in formal medical training or in common medical journals. Insight into this phenomenon, termed Simpsonʹs paradox, may prevent clinicians from drawing faulty conclusions about vitamin D deficiency and heart disease.