Stanford.edu - Skin cancer patients who avoid the sun are three times more likely to have vitamin D deficiency than healthy people, according to a new study led by researchers at the Stanford University School of Medicine.
Vitamin-D deficiency puts adults at a higher risk for cardiovascular disease, autoimmune disease (specifically multiple sclerosis), some cancers and even death. Extremely low vitamin D levels in children causes rickets, a serious bone disease. In adults, it can cause a condition known as osteomalacia, or bone pain.
Jean Tang, MD, PhD, assistant professor of dermatology, said physicians need to strike the right balance in helping their skin cancer patients avoid sunlight - the primary way in which vitamin D is produced by the body - while finding other ways to maintain their vitamin D levels.
“There is a chance that we are inadvertently putting some of our patients at risk for vitamin-D deficiency because they’re avoiding sunlight, they’re putting on sunscreen, they’re staying in the shade,” said Tang, who is the principal investigator of the study published in the October 2010 issue of Archives of Dermatology. “Basal cell skin cancers, the most common type of cancer in the United States, are generally not lethal. So it’s important for patients to look after their overall health.”
Vitamin D is synthesized in the body when UVB rays from the sun react with a precursor molecule in the skin called 7-dihydrocholesterol. Dermatologists advise skin cancer patients to avoid sun exposure, so in these patients are exposed to fewer UVB and therefore produce less vitamin D.
For the study, researchers looked at vitamin D levels in the blood plasma of 41 skin cancer patients with basal cell nevus syndrome (BCNS) who were participating in a clinical trial, and compared them to the vitamin D levels of people without the disease. BCNS is a genetic disease in which patients develop dozens or hundreds of basal cell carcinoma tumors that look like protuberant moles or shiny, ulcer-like bumps on their skin. Treatment involves surgical removal and comprehensive sun protection.
Tang and her colleagues improved on past studies by matching each BCNS patient to data from a control population of people of comparable age, sex, body mass index, geographic residence and Fitzpatrick skin type (a measure of melanin pigmentation, or skin color). The data for the control population came from the 2007 Nutritional & Health Examination Survey by the U.S. Centers for Disease Control and Prevention.
Not surprisingly, the researchers found that BCNS patients who stayed out of the sun were more vitamin D deficient than people in the control population.
The American Academy of Dermatology does not recommend more sun exposure as a way to prevent vitamin D deficiency in those at risk for skin cancer. Taking dietary supplements made from oily fish or sun-exposed sheep’s wool provides the same type of vitamin D, namely vitamin D3, as sun exposure. Appropriate dosage is important; taking too much vitamin D may raise calcium levels and lead to kidney stones.
The researchers also found that patients were not following medical advice as diligently as they had expected. BCNS patients had higher vitamin D levels in summer than in winter, which means they were not effectively avoiding sunlight in the summer months. “If these guys who have hundreds of tumors are not listening to us, who is?” said Tang.
Having dark skin was another risk factor for vitamin D deficiency, because skin pigment absorbs sunlight and reduces the amount of UVB radiation available to react with the skin’s 7-DHC precursor molecules. Being older was a risk factor for vitamin D deficiency because the amount of 7-DHC in the skin decreases with age.
Overweight people were also at increased risk because vitamin D is fat-soluble. It gets stored in fatty tissue instead of circulating in the blood where it is needed.
“Vitamin-D deficiency may also be a problem in patients with sporadic skin cancers and not just patients with BCNS,” said Tang. “I care about this second group of patients very much because skin cancer is so common in the United States.”