NOS3 and vitamin D deficiency: The impact of vitamin D deficiency in cerebrovascular diseases may adversely affect endothelial cell function and vascular homeostasis through pleiotropic pro-oxidant (endothelial nitric oxide synthase (eNOS), reactive oxygen species (ROS), upregulation of NADPH oxidases (NOXs)) and pro-inflammatory effects (inflammatory cytokines, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-B), matrix metalloproteinases (MMPs)).