BOSTON, Feb. 15 (UPI) -- Despite concerns about skin cancer, researchers suggested Friday that too little sunshine might increase a person's risk of developing several other malignancies, such as colon, prostate and breast cancers.
"As many as 30,000 people a year in the United States die of cancer that may have arisen from vitamin D deficiency," said William Grant, an independent researcher in Newport News, Va. "About 70,000 people a year develop cancer because of lack of vitamin D."
During a news briefing at the annual meeting of the American Association for the Advancement of Science, Grant said the major reason for vitamin D deficiency was lack of ultraviolet-B radiation -- one type of radiation generated by sunlight and absorbed through the skin.
"If it takes you about 30 minutes of unprotected exposure to the sun to give you a sunburn," said Dr. Michael Holick, professor of medicine and dermatology at Boston University School of Medicine, "then you should try to get 5 to 10 minutes of sunlight on your face and hands each day."
He said that amount of exposure will give the body enough UVB to allow the skin to produce enough activated vitamin D to maintain normal functions. The amount of sunlight needed varies depending on the pigment of the skin, the season of the year and the time of the day, he said.
Holick said scientists believe activated vitamin D regulates cell growth in the body, preventing cells from proliferating abnormally and causing cancer. "Vitamin D is critically important for cellular health," he said.
He said the new work presented by Grant appears to support other studies, which showed increased rates of gastrointestinal, breast and other cancers in people who have low levels of vitamin D.
"There is an epidemic of vitamin D deficiency in the United States," he said at the news briefing. He estimated as many as 50 percent of the adult population of Boston is deficient in vitamin D and added that a study of medical school residents -- "who never see the light of day" -- found that 37 percent of these 23- to 32-year-olds were deficient in vitamin D.
Grant said his estimates of vitamin D deficiency and lack of UVB and resulting increases in cancer were developed through study of cancer mortality data maps and overlapping maps produced by NASA satellites showing UVB radiation distribution across the United States.
When he looked at the correlation between malignancy and low UVB exposure, he saw a high risk of developing breast cancer, ovarian cancer and colon and rectal cancer in both men and women.
Holick said people should allow sun exposure without sunscreen for a brief amount of time and then they should apply a standard amount of sunscreen if they are planning a day on the beach or in the outdoors. He said the body has powerful abilities to turn UVB into what it needs to keep cells in check.
Holick said there is no evidence to suggest vitamin D supplementation can fight cancer once it develops -- only that it may prevent the cancer from occurring.
He said getting UVB radiation from the sun may be better than vitamin D supplementation because the sun's rays also cause certain other photodynamic changes that may be helpful to the body and that large amounts of vitamin D -- far more than the recommended daily allowances -- may be required to equal what a short walk in the sun can produce.