Vitamin D is largely misunderstood because very few people need it in the form of a supplement alone. The ultraviolet rays from the sun convert skin oil to vitamin D. Too much vitamin D is called hypervitaminosis D. Actually, it is a deficiency of "vitamin F", vitamin D's antagonist.
Vitamin D picks up calcium from the gut and puts it into the blood. "Vitamin F" takes it from the blood and puts it into the tissues.
Suppose you get D and no F. Your blood calcium level will increase at the expense of the tissue calcium level, because D not only picks up calcium from the gut, but in a deficiency of F, it also brings calcium from the tissues back into the blood.
That's why people who are in the sun a lot get thick skin if they don't eat enough "Vitamin F", which is primarily in oils. They get hives and sunstroke. Sunstroke involves high blood calcium levels with low tissue calcium levels. Excess vitamin D from extreme exposure to the sun is known to cause cancer. You might have read articles that say you should stay of the sun, that sunshine is hazardous to health. Well, it's only dangerous to people who are "Vitamin F" deficient. Standard Process is the one of the only companies that calls this factor "Vitamin F".
As said earlier, "Vitamin F" also delivers calcium into the tissues from the blood. What does this do? Without this mechanism working properly, there's tissue calcium starvation with resulting itching of the skin. Anybody whose skin itches, look out! You need Cataplex F and Calcium Lactate.
Take Calcium Lactate to be sure you have enough calcium, and Cataplex F to deliver the calcium into the tissues.
This can go to any degree. Hives that people get from being out in the sun a lot - the big welts that form around the tender parts of the body - this is a symptom of tissue calcium deficiency. If you take Cataplex F, the calcium that is already in their blood is delivered into the tissues and the welts clear up. Canker sores & Cold Sores that develop on the inside of and around the mouth are also related to tissue calcium starvation. Cold sores are caused by a herpes simplex virus. Once you have the virus, you will for the rest of your life, but if your tissue calcium stays sufficiently high, the virus never forms the canker sores. It is not such a bad thing to have them because they reveal your tissue calcium level. As soon as your tissue calcium level goes down, they pop out and you know you need Calcium Lactate and/or Cataplex F.