It has been scientifically proven that humans have evolved in our natural environment such that we can obtain 90% of the vitamin D we need from the sun, through the skin. Eating certain foods, such as oily fish, also provides vitamin D, but it is mainly sunlight that stimulates the production of vitamin D. This natural process starts in the skin after exposure to sunlight, and particularly UVB (which, in addition to UVA, is a component of sunlight). Here we are talking about the human form of the vitamin, D3, which can only be generated by sunlight. The body itself regulates this process, breaking down any excess that is produced. This is in contrast to the oral intake of supplements, in which the plant form, vitamin D2, is introduced directly into the body. A large excess of this vitamin can result in poisoning, because the body cannot break it down. Nevertheless, the likelihood of a vitamin D insufficiency is greater than that of an overdose.