There is a lot of debate about the optimal dose of vitamin D and it is one of the most common questions people ask me.
The current recommended daily allowance for vitamin D is a mere 600 IU (15 mcg) daily. Prominent experts in this area claim that dose is based on erroneous calculations and is only about one tenth of what people should be taking . There are also popular books that suggest taking 50,000 IU per day. I’m not kidding.
We know that for just about any health condition that pertains to vitamin D status, the dose-benefit relationship is usually a U-shaped curve. That means too little is associated with problems, as is too much. But where is the sweet spot? And how do we know that optimal intake, or even blood levels determined by population-based studies, are really optimal for any one individual? The answer is… it depends. Specifically, it depends on your intake of vitamins K2 and A.
It’s obvious that having vitamin D deficiency is not a good thing. The issue here is the effect of excess, and how to avoid that.
Vitamins K2 and A
One of the main actions of vitamin D is to enhance calcium absorption. The more we take, the more calcium we absorb, indefinitely . So the rare problems we see with vitamin D toxicity appear as calcium deposits in soft tissues, such as kidney stones and hardening of the arteries. Vitamin K2 prevents calcium from depositing in soft tissues, and vitamin A naturally keeps vitamin D in check . See chapter 7 of my book Vitamin K2 and the Calcium Paradox for the full story.
Take the following extreme example of vitamin D excess. I heard from one person who had been taking the whopping 50,000 IU daily (without K2 or A) for six months when he suffered a heart attack. His doctors said they had never seen the amount of arterial calcification that he had around his heart. It is unlikely to see the downside of vitamin D in doses under 10,000 IU daily , but I wouldn’t take D in any amount without taking vitamin K2 and vitamin A with it.
Debate continues about the optimal dose of vitamin D – and likely varies per person – but ultimately the safety and optimal efficacy depend less on the amount you are taking than it does on your intake of the nutrients that work with it, like vitamins A and K2.
 Veugelers PJ, Ekwaru JP. A Statistical Error in the Estimation of the Recommended Dietary Allowance for Vitamin D. Nutrients. 2014; 6:4472-4475.
 Jones G. Pharmacokinetics of Vitamin D toxicity. 2008 Aug; 88(2):582S-586S.
 Kurnatowska I, Grzelak P, Masajtis-Zagajewska A, Kaczmarska M, Stefańczyk L, Vermeer C, Maresz K, Nowicki M. Effect of Vitamin K2 on progression of atherosclerosis and vascular calcification in non-dialyzed patients with chronic kidney disease stages 3-5. Pol Arch Med Wewn. 2015; 125(9):631-40. Epub 2015 Jul 15.