It is plausible that patients undergoing chemotherapy less likely experience sunlight exposure, less able to absorb Vit D due to subclinical mucositis and less able to metabolize 25(OH)D into inactive compounds such as 24,25(OH)2Vit D through the activation of CYP3A4 or other metabolizing enzymes. This evidence concerns the gene CYP3A4 and mucositis.