Vitamin D is a very safe supplement, and the Linus Pauling Institute reports there are no documented cases of vitamin D overdose due to sunshine exposure. As you possibly know, vitamin D is the "sunshine vitamin" because that's the source of most vitamin D in humans. However, in rare instances, excessive intake of vitamin D supplements has produced serious health consequences.
Vitamin D Toxicity
Vitamin D toxicity or hypervitaminosis D is extremely rare. According to the July 2007 issue of the "New England Journal of Medicine," you can ingest well in excess of 10,000 IU of vitamin D per day for five months without any problem whatsoever. However, doses of more than 50,000 IU per day can induce a condition known as hypercalcemia. In hypercalcemia, abnormally high serum calcium levels in the blood could result in bone loss, kidney stones, and calcification of organs like the heart and kidneys if untreated over a long period.
Vitamin K Deficiency
The December 2007 issue of "Medical Hypotheses" discussed additional symptoms of hypervitaminosis D, including loss of appetite, nausea, vomiting, high blood pressure, kidney malfunction and failure to thrive. However, the authors took issue with the notion that the toxicity of vitamin D is attributable to its induction of hypercalcemia. They pointed out that hypervitaminosis D symptoms such as anorexia, lethargy, growth retardation, bone resorption, soft tissue calcification and death has no association with hypercalcemia in animal studies. The authors argued that the toxic effects of vitamin D overdose occur because it depletes the body of vitamin K.
Anecdotal Evidence
As you can imagine, no systematic studies have examined vitamin D intoxication in humans for ethical reasons. Nonetheless, the August 2008 issue of the "American Journal of Clinical Nutrition" reports on anecdotal evidence collected by medical researchers on vitamin D overdose. One report documented a cluster of 35 patients diagnosed with hypercalcemia resulting from drinking over-fortified milk purchased from a home delivery dairy. Thirty-two percent of the patients suffered anorexia, 27 percent suffered weight loss, 27 percent experienced weakness and 21 percent showed fatigue and disorientation. Fifty-nine percent of the patients were ill enough for hospitalization.
Physician Error
Researchers reporting in the May 2011 issue of the "Oman Medical Journal" explained that in the Kashmir region of India, vitamin D deficiency is common. As a result, physicians commonly prescribe vitamin D supplementation and occasionally over-prescribe. The researchers reported on 10 cases of hypercalcemia induced by over-prescribing vitamin D during the course of 10 years. The most common symptoms were polyuria, which is the medical term for excessive urination; poldispsia, which is excessive thirst; and oliguria, or abnormally low urine output. All of these symptoms link with kidney dysfunction, which hypercalcemia also can cause.
References
- Linus Pauling Institute; Micronutrient Ctr.: Vitamin D
- "New England Journal of Medicine"; Vitamin D Deficiency; Michael Holick; July 2007
- "Medical Hypotheses"; Vitamin D Toxicity Redefined: Vitamin K and the Molecular Mechanism; Christopher Masterjohn; December 2007
- "American Journal of Clinical Nutrition'; Pharmacokinetics of Vitamin D Toxicity; Glenville Jones; August 2008
- "Oman Medical Journal"; Vitamin D Toxicity in Adults: A Case Series from an Area with Endemic Hypovitaminosis D; Parvaiz Koul et al.; May 2011
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