It is the craziest thing.
The notion of vitamin D being easily and readily toxic has grabbed hold of many people, including my colleagues who were taught that vitamin D was toxic in medical school based on the skimpiest (and often misinterpreted) observations in a handful of unusual cases.
In my practice and in the Track Your Plaque program, we routinely use doses of 2000-10,000 units per day, occasionally more. We are guided by blood levels of 25(OH) vitamin D3. I have personally never witnessed vitamin D toxicity.
Here's an interesting graph from Dr. Reinhold Vieth. Those of you familiar with the vitamin D argument know that Dr. Vieth is among the few genuine gurus in the vitamin D world.
From Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr 1999;69:842-856. (Full text is available without charge.)
In the graph, the X's represent toxicity; circles fall within the non-toxic range. (Toxicity is generally defined as a level sufficient to raise blood calcium levels, "hypercalcemia.") Note that the 25(OH) vitamin D3 levels are given in nmol/L; to convert to ng/ml units that are customary in the U.S., divide the nmol/L value by a factor of 2.5.
You will notice that toxicity is virtually unheard of until the dose exceeds 10,000 units per day. Beyond 10,000 units per day, the curve heads upward sharply and toxicity does become a possibility, though not an absolute (since there are circles above 10,000 units).
You may also notice that the curve is relatively flat from vitamin D doses between 200 units and 10,000 units (log scale on x axis; arithmetic scale on y), the range of most common doses for vitamin D supplementation.
Another perspective on vitamin D blood levels is to examine the blood levels of people who are young and obtain plentiful sun exposure. Lifeguards, for instance, have blood levels of 84 ng/ml (210 nmol/L) without ill-effect. (Sun exposure cannot generate vitamin D toxicity, because of a feedback safety mechanism in skin.) While this may not represent an ideal level since they represent an extreme, it does provide reassurance that such levels are non-toxic. I also point out these levels occur in the youthful since most people lose 75% or more of vitamin D activating capacity in the skin by their 70s. Most of us over 40 are kidding ourselves if we think that a suntan provides sufficient vitamin D.
Keep in mind that it is not necessarily the dose of vitamin D that is toxic, but the blood level it generates. I take 10,000 units of vitamin D as a gelcap per day to maintain my blood level between 50-60 ng/ml (125-150 nmol/L). This strategy helps me keep my HDL in the 70-80 mg/dl range, my blood sugar around 90 mg/dl, my blood pressure <120/80, and I no longer experience colds nor winter "blues."
Copyright 2008 House, MD