The most common side effects of vitamin D include fatigue, weakness, dry mouth or a metallic taste in the mouth, loss of appetite, nausea and vomiting, according to WebMD. Most people do not experience side effects with vitamin D, unless they take too much.
Although vitamin D side effects are rare, according to WebMD, there are certain situations that may lead to additional side effects and repercussions. A person who takes an extremely high dose of vitamin D, approximately 4000 units daily or more, for a long period, may have some excessively high levels of calcium in the blood.
High calcium levels in the blood can increase the risk of the hardening of the arteries (atherosclerosis) for people with pre-existing serious kidney disease or, in some cases, increase the chance for kidney stones. A high dose of vitamin D can also increase the calcium levels in the blood for individuals with sarcoidosis, histoplasmosis, over-active parathyroid glands, lymphoma, or tuberculosis. These people are all at risk for developing too much calcium in the blood after taking too much vitamin D for an extended period.
While vitamin D is typically safe during pregnancy and nursing, WebMD states women should not take more than 4000 units per day as higher doses can cause damage to the infant.