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Ask a Scientist -- Dr. John Cannell

Questions and Answers with Dr. John J. Cannell, M.D.
Executive Director, Vitamin D Council

Since the start of GrassrootsHealth, two of the most common questions asked have been "How much vitamin D should I take?" and "Is vitamin D toxic?" This newsletter provided detailed answers to each of those questions. Here are the questions you asked about toxicity…

Q: There are some conditions, such as sarcoidosis, where hypersensitivity to vitamin D/vitamin D toxicity is a concern. Should people with these conditions avoid all vitamin D supplements? 

A: Yes, unless they are under a physician’s care. While nothing exists in the literature, Professor Michael Holick has found he can get his sarcoidosis patients up to 30 ng/ml without hypercalcemia by carefully adjusting the dose of vitamin D.

Q: Surely toxicity is greatly influenced by the consumption of vitamin K2? Why do we not hear more on the subject of Vitamin K2 when clearly there is so much research to show that it is essential to take it with D3 especially for the distribution of calcium and avoidance of atherosclerosis and kidney stones?


A: Actually there is not much research on the interactions of vitamin D and vitamin K in toxicity other than those hypothesized by the mechanism of action of the two vitamins. An unusual hypothesis exists that it is vitamin K deficiency that causes the symptoms of vitamin D toxicity:

Vitamin D toxicity redefined: vitamin K and the molecular mechanism.
Masterjohn C.
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Animal studies indicate vitamin K reduces vascular calcification and human dietary studies indicate it does. However, the first randomized controlled trial testing that hypothesis is ongoing. They are using 5,000 mcg/day of vitamin K1. Remember about 5 to 25% of vitamin K1 is metabolized to vitamin K2 in the body so the study should give us some answers about both vitamin K1 and K2.

Vitamin K1 to slow vascular calcification in haemodialysis patients (VitaVasK trial): a rationale and study protocol.
Krueger T., et al.
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