The value of vitamins is not infrequently underestimated by doctors. Nevertheless, researchers continue to verify that vitamins can be beneficial in treating diseases. Vitamin D has been shown to be effective for psoriasis, a potentially disabling skin condition. In one study, 90% of psoriasis patients improved markedly when a form of Vitamin D was applied to their skin.The National Institutes of Health has been interested in Vitamin C, and in September, it sponsored a conference on the vitamin's usefulness in treating cancer. Dr. Linus Pauling, the Nobel Prize-winning scientist, has argued for years that cancer patients live longer when treated with high doses of Vitamin C. In one study, he and a colleague showed that patients who received Vitamin C in addition to other treatments, such as chemotherapy or radiation, lived 16 times as long as patients who only received the generally accepted medical treatment.