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Response

I would like to thank Dr Eveleigh for his excellent comments regarding vitamin D toxicity. Indeed there have been cases of toxicity with vitamin D2 (ergocalciferol) resulting in hypercalcemia,¹ deafness,² and even death.³ Vitamin D2 that is not quality controlled (imported and unregulated) might result in toxicity as well.⁴ I always recommend that my patients look for a Drug Identification Number (DIN) on the vitamin D bottle.

There are no reported cases of toxicity from vitamin D3 (cholecalciferol) in humans, but vitamin D3 when improperly mixed into animal feed has caused death.^5,6 This lack of reported cases might simply be a reflection of the smaller dose (400 to 1000 IU) tablets of vitamin D3 and the fact that one is unlikely to ingest 50 or so tablets a day.

Repletion of vitamin D with vitamin D2 is common practice, and vitamin D2 can be used safely when monitored to achieve normal levels of 25(OH)D. This might take 2 to 3 months, as discussed in your letter and in my paper, because the half-life is about 2 weeks. Using vitamin D3 (1000 to 5000 IU) daily, depending on the level of deficiency, will also achieve this goal. I also agree that the goal is to achieve levels of 25(OH)D higher than 100 nmol/L, preferably 100 to 125 nmol/L.

My concern regarding vitamin D2 is that it is a synthetic analogue and might interact with the vitamin D receptor differently in various cell systems. It has been reported that vitamin D3 might improve glycemic control.⁷ Vitamin D2 has been reported to cause worsening of glycemic control in people of East Indian descent.⁸ Is this because of vitamin D receptor polymorphism, or because of enhanced 24-hydroxylase enzyme activation, or is it due to how vitamin D2 interacts with the receptor? Until this has been sorted out, I feel safest using vitamin D3. There are about 2000 synthetic analogues of vitamin D. The search is on for one that can cross the blood-brain barrier to treat certain types of brain cancers without causing hypercalcemia.⁹ But then again, what other effects would this compound have? There are still so many unknowns.

The first step is to recognize that most Canadians do not get enough vitamin D, especially in the winter months, because of where we live. This recognition might reduce the need for expensive drugs to treat various conditions and might improve the well-being of many Canadians.

An ounce of prevention is worth a pound of cure.

	References

TOP References

 

1. Paterson CR. Vitamin-D poisoning: survey of causes in 21 patients with hypercalcaemia. Lancet 1980;1(8179):1164-5.[Medline]
2. Cohen HN, Fogelman I, Boyle IT, Doig JA. Deafness due to hypervitaminosis D. Lancet 1979;1(8123):985.[Medline]
3. Blank S, Scanlon KS, Sinks TH, Lett S, Falk H. An outbreak of hypervitaminosis D associated with the overfortification of milk from a home-delivery dairy. Am J Public Health 1995;85(5):656-9.[Abstract/Free Full Text]
4. Barrueto F Jr, Wang-Flores HH, Howland MA, Hoffman RS, Nelson LS. Acute vitamin D intoxication in a child. Pediatrics 2005;116(3):e453-6.[Abstract/Free Full Text]
5. Heinritzi K, Hänichen T, Rambeck W, Hermanns W. [Vitamin D3 poisoning—case report]. Dtsch Tierarztl Wochenschr 2000;107(12):477-80.[Medline]
6. Roder JD, Stair EL. An overview of cholecalciferol toxicosis. Vet Hum Toxicol 1999;41(5):344-343.[Medline]
7. Borissova AM, Tankova T, Kirilov G, Dakovska L, Kovacheva R. The effect of vitamin D3 on insulin secretion and peripheral insulin sensitivity in type 2 diabetic patients. Int J Clin Pract 2003;57(4):258-61.[Medline]
8. Taylor AV, Wise PH. Vitamin D replacement in Asians with diabetes may increase insulin resistance. Postgrad Med J 1998;74(872):365-6.[Abstract/Free Full Text]
9. Elias J, Marian B, Edling C, Lachmann B, Noe CR, Rolf SH, et al. Induction of apoptosis by vitamin D metabolites and analogs in a glioma cell line. Recent Results Cancer Res 2003;164:319-32.[Medline]

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Vitamin D supplementation

Bruce Eveleigh
CFP 2007 53: 1435. [Full Text]  

This Article Full Text (PDF) Rapid Responses: Submit a response Alert me when this article is cited Alert me when Rapid Responses are posted Alert me if a correction is posted Services Email this article to a friend Related articles in CFP Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Schwalfenberg, G. Search for Related Content PubMed PubMed Citation Articles by Schwalfenberg, G.