Vitamin D and calcium supplements were associated with a 50 percent reduction in the risk of melanoma in women at high risk of developing this life-threatening skin cancer, researchers from Stanford University report in the Journal of Clinical Oncology.
Led by Jean Tang, MD, PhD, the researchers analyzed data from the Women's Health Initiative, a randomized clinical trial involving 36,282 postmenopausal women who received either placebo or 400 international units of vitamin D and 1,000 milligrams of calcium carbonate per day.
"Our results include the first positive cancer-reducing effect seen from the calcium plus vitamin D trial," said Teresa Fu, MD, a co-author of the study.
Shining light on the sunshine vitamin
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
D and the big C
The link between vitamin D intake and protection from cancer dates from the 1940s when Frank Apperly demonstrated a link between latitude and deaths from cancer, and suggested that sunlight gave "a relative cancer immunity".
Since then there have been numerous studies suggesting associations between vitamin D and lower risks of certain cancers.
There is growing evidence that 1,25(OH)2D has anticancer effects, but the discovery that non-kidney cells can also hydroxylate 25(OH)D had profound implications, implying that higher 25(OH)D levels could protect against cancer in the local sites.
The new study adds to this body of science, suggesting a role for the vitamin-mineral combination for skin cancer.
Dr Tang and her co-workers focused on non-melanoma skin cancer, as people with this generally non-fatal disease are more likely to develop the more lethal illness — melanoma. Non-melanoma skin cancers, such as basal cell or squamous cell cancers, are the most common forms of skin cancer.
Results indicated that women who once had non-melanoma and took the calcium-vitamin D combination developed 57 percent fewer melanomas than women with similar histories receiving the placebo.
A limitation of the study design was that women in the placebo group were allowed to take as much vitamin D as women in the calcium and vitamin D group. According to the researchers, this may have masked many of the potential benefits of vitamin D.
The researchers said that the results should be interpreted with caution but the findings “spur us to do more studies”, said Tang.
Source: Journal of Clinical Oncology
Published online ahead of print, doi: 10.1200/JCO.2011.34.5967
“Calcium Plus Vitamin D Supplementation and the Risk of Nonmelanoma and Melanoma Skin Cancer: Post Hoc Analyses of the Women's Health Initiative Randomized Controlled Trial”
Authors: J.Y. Tang, T. Fu, E. LeBlanc, J.E. Manson, D. Feldman, E. Linos, M.Z. Vitolins, N.C. Zeitouni, J. Larson, M.L. Stefanick