Vitamin D regulates the calcium levels in blood. A prolonged overdose of this vitamin, also known as vitamin D toxicity, causes calcium levels to rise over a certain limit, resulting in complications, such as coma and cardiac arrest. So, how much vitamin D will cause toxic levels of calcium to build up in the blood? Are the baseline levels, which are currently considered normal, accurate? John Cannell, a prominent researcher and vitamin D advocate, provides an interesting insight into this topic in his article titled, “the difference between two “normals”,” suggesting that the references taken for calculating these levels in the USA are faulty!