Vitamin D, a fat-soluble vitamin, is essential for bone health, absorbing calcium, modulating cell growth, boosting the immune system and reducing inflammation. You can obtain vitamin D from three main sources: certain foods such as fatty fish and fortified juices or cereals; direct sun exposure and supplements. Although overdose is not common, excessive consumption of vitamin D supplements can result in overdose. Overdose of vitamin D is potentially serious but medically treatable, according to the Mayo Clinic.
The body gets about 80 to 90 percent of its vitamin D from direct sun exposure. However, if you live in Canada or the northern United States, limited sun exposure may warrant the use of vitamin D supplements. Doctors may also prescribe vitamin D for people over 65 as they are less likely to spend time in the sun and have fewer receptors to convert sunlight to vitamin D. The Institute of Medicine recommends 600 IU (international units) of vitamin D daily for children and adults up to the age of 70. For adults over the age of 70, 800 IU is recommended daily.
Overdose of vitamin D causes a condition called hypervitaminosis D. It can produce a variety of symptoms such as nausea, vomiting, lack of appetite, constipation, muscle weakness, headache, anorexia, irritability, and bone pain. Too much vitamin D can also cause an increase of calcium in the blood, which can cause vascular and tissue calcification. Increased calcium in the blood can lead to eventual damage to heart, blood vessels and kidneys.
It is unsafe to take vitamin D in doses of 2000 IU per day for long periods of time. This can lead to a calcium spike in the blood, which can cause health implications as discussed above. High doses are also unsafe for pregnant women as it may cause harm to the developing fetus. People with kidney disease, sarcoidosis, histoplasmosis and lymphoma have a higher risk of increasing calcium in the blood with vitamin D overdose. Taking thiazide-type diuretics with vitamin D supplements may create overdose risks.
To stop vitamin D toxicity, the doctor may ask you to stop taking vitamin D supplements or restrict calcium intake. In severe cases, you may require hospitalization.
It is advisable not to take higher doses of vitamin D unless prescribed. Doctors may recommend higher doses of vitamin D for treating medical conditions such as vitamin D deficiency. Even then, such doses should be given under medical supervision.