Vitamin D-2, a form of vitamin D, should be taken in doses smaller than 4,000 units. If higher amounts of vitamin D-2 are taken for an extended time, possible side effects include headache, increased calcium levels, a metallic taste in the mouth and nausea, according to WebMD.
Vitamin D-2 is taken orally to prevent osteoporosis, bone fractures and falls, states WebMD. Other uses include treatment of multiple sclerosis and muscle pain caused by other medications, as well as cancer and flu prevention. Appropriate daily dosage is dependent on age and varies between 400 units to 1,000 units.
If vitamin D-2 is taken in doses higher than 4,000 units per day for long periods of time, calcium levels in the blood may rise. This increase in calcium may cause hardening in the arteries of people who have kidney disease, possibly leading to kidney stones, kidney failure or a related bone disease. An excess of vitamin D-2 and the resulting increase in calcium levels may also cause kidney problems in people with sarcoidosis, histoplasmosis, hyperparathyroidism, lymphoma and tuberculosis. It is also recommended that pregnant and nursing women take no more than 4,000 units of vitamin D-2, since higher doses may affect the health of the child, according to WebMD.