Actually, you need vitamin D regularly. It does not last the whole winter either - hence more viral infections and depression in the winter. It is very hard to overdose on vitamin D3. You would have to have a level over 100 for 25-hydroxyvitamin D. In America, White people might have around 17-20 ng/ml of the precursor while Af-Am is closer to 9-11 ng/ml. A good number would be about 30, though some people get additional benefits at 60-70 ng/ml, likely due to polymorphisms of the VDR receptor. As a personal theory, I have a feeling those with the polymorphisms are more likely to develop autism, since they need more D to get the same results as normal people, and D apparently plays a role in removing toxins from the body (that is just a mild hypothesis, and I have no proof).<quoted text>
Vitamin D is a Fat-Soluble Vitamin. Many health articles state Fat-Soluble Vitamins are stored for long periods of time and we only need small amounts to avoid toxicity while scientific articles and studies state supplements are recommended for these same Vitamins due to low Vitamin D levels. Once your levels are sufficient, you wouldn't need to spend the same amount of time in the sun unless you remain out of the sun for a long period of time. The articles are written as if darker skin is unable to reach sufficient levels naturally hence the need for supplements. Those who are unable to utilize Vitamin D after sun exposure need the supplements.
"In medicine, a 25-hydroxy vitamin D (calcidiol) blood test is used to determine how much vitamin D is in the body. The blood concentration of calcidiol is considered the best indicator of vitamin D status."
As for the sun, it is virtually impossible to overdose on vitamin D directly from the sun. Overdose has to be done by iatragenic means. Once you have enough, the enzymes that do the conversion from the skin shut down. So you basically would have to ingest or inject an overdose. And yes, it is cumulative - especially when taken orally or injected. The Vitamin D Council site ran into this. They were suggesting a liquefied form of D3 on the air. Soon after, they were threatened by an attorney with a lawsuit. His 25-hydroxyvitamin D levels were off the chart. The advice given was not bad. It turned out that the company the lawyer got the stuff from had a recall, and he had a product with the affected lot number. They made a serious error and forgot to dilute it for that batch. The D Council folks told him how to get his levels down and when to start taking it again. But that is a very rare situation.
Vitamin D is not just for the bones, but affects many systems. You might have enough for the bones but not enough for other parts of the body. If you have adaptations to the parathyroid gland, then you won't "need" as much for bones, but that has no guarantee on the rest of you.
Now what was mentioned earlier on blood calcium does seem to be a matter of concern and should be studied. You don't want excessive levels in the arterial walls nor in the brain.
Most Americans are sun-phobic, and even African Americans are now being told to use heavy sunscreen since more are getting skin cancer, even with all the melanin. And the melanin and ethnic stereotypes make it harder to detect. That conclusion was just published. And the same researchers say they will need to take lots of vitamin D since Af-Ams are likely already low. Like I said before, skin cancer across racial lines is similar to breast cancer across gender lines, and BP think they are immune to one, and men to the other. So that public perception makes it harder for people to admit they could have a problem or to see their doctor.