IIRC, it's the same with Vitamin C since it's water soluble (i.e. excess escapes through your urine). Just note that -- like everything -- it is possible to overdose, so don't down a whole bottle of Vitamin C/D pills in a single go. It's just in these cases your body can readily deal with excess (as long as it's not too much excess).

Vitamin D is a fat soluble vitamin, like Vitamins A, E, and K. It does accumulate in the fat tissue. An excess of Vitamin D is not simply disposed of in the urine, like Vitamin C or the B-complex.

Interestingly, although it is now evident that Vitamin D insufficiency and deficiency is higher in the general population than previously realized, it is often worse in those with higher levels of fat in the body.

  "CONCLUSIONS: Obesity-associated vitamin D insufficiency is likely due to the decreased bioavailability of vitamin D(3) from cutaneous and dietary sources because of its deposition in body fat compartments."

above from Am J Clin Nutr. 2000 Sep;72(3):690-3. Decreased bioavailability of vitamin D in obesity.

Vitamin D toxemia can occur. One of the more common symptoms is nausea, and if the toxemia persists, calcification of soft tissue and formation of kidney stones can result. Vitamin D is needed for proper intestinal absorption of calcium, so excess Vitamin D can throw off proper mineral balances in the body.

Likelihood of toxemia is rare for Vitamin D, however.

Consider that a healthy individual can obtain 10,000 IU or more of Vitamin D produced by their own skin from being exposed to the sun for 20 to 30 minutes. The amount of Vitamin D in a standard multivitamin supplement is rarely more than the current US RDA, which is only 400 IU. So even people taking higher dose Vitamin D supplements of, say 5000 IU, are not really mega-dosing/"going Linus Pauling" with their Vit. D.

Also, that current RDA of 400 IU is now considered by many scientists and health professionals to be too low. It may simply be the minimum amount needed to prevent rickets (known in adults as osteomalacia). Now it is known that it is needed for more than just bone development and maintenance, as Vitamin D receptors have been found throughout the body; some reports say virtually everywhere.

Reading through the information at http://vitamindcouncil.org , it appears that to achieve what is now considered an optimal Vitamin D level in the body, people generally need more sun and/or supplementation.

In the news within the last year or so, a study reported that even 50% of Hawaiians were low in Vitamin D. In modern society, I guess that walking from the car to the office daily just doesn't cut it for sun exposure ;)

> ...a healthy individual can obtain 10,000 IU or more of Vitamin D produced by their own skin from being exposed to the sun for 20 to 30 minutes.

It seems like that 10,000IU/.5hr dose would be surface-area dependent. Are the face, hands, and maybe forearms sufficient? Or does that number depend on, erm... _all_ of the skin being exposed?

I read somewhere that 15 minutes direct sun exposure per day in a t-shirt between 11 AM and 3 PM is sufficient. Obviously that has to depend on the latitude of your location so I'm not sure how accurate or meaningful it is. And it does depend on the color of your skin. The darker your skin the more sun you need to get the same amount of vitamin D.

It'd take more than just a bottle of vitamin C pills, I think--it's one of the least toxic substances known. The LD50 on vitamin C is probably about two pounds of pure vitamin for an average adult.

It's probably easier (and certainly more common) to overdose on water.