Scanning some online newspapers last week, my eye was caught by reports of a couple of studies concerning vitamin D and cancer. The link between the two is not new.
There is a huge stack of evidence that shows an association between higher levels of vitamin D and lower risk of several different forms of cancer. The two studies I write about today just add to this stack but are interesting nonetheless.
The first of these studies was published in September in the British Journal of Cancer, and focused on the relationship between vitamin D levels and colon cancer.  The study assessed more than 1,000 individuals diagnosed with colon cancer between 1986 and 2004. Individuals with the highest levels of vitamin D were found to be at half the risk of dying from colon cancer during the study than individuals with the lowest levels.
In addition, overall risk of mortality was reduced in those with highest vitamin D levels (the risk reduction was 38 percent).
In the second study, researchers assessed the relationship between vitamin D levels and malignant melanoma.  Part of this study followed 871 individuals for an average of almost five years. Higher vitamin D levels were associated with thinner tumors when diagnosed.
Also, higher vitamin D levels were found to be associated with reduced risk of relapse and enhanced survival.
Most of our vitamin D requirements come from the action of sunlight on the skin. So, in theory, sunlight exposure could be good news for those wishing to protect themselves from an untimely death due to melanoma.
This may seem somewhat counterintuitive since we are traditionally warned that sunlight causes melanoma. However, this is not as assured as we have been led to believe.
The other thing to bear in mind is that even if sunlight does increase the risk of melanoma, it likely reduces the risk of several other cancers, including colon cancer.
Awhile back some Norwegian researchers calculated that for each life saved by reducing sunlight exposure (as a result of reduced skin cancer incidence), 10 lives would be lost due to increased incidence in other cancers. 
1. Ng K, et al. Prospective study of predictors of vitamin D status and survival in patients with colorectal cancer. British Journal of Cancer, 2009; 101(6): 916–23.
2. Newton-Bishop JA, et al. Serum 25-Hydroxyvitamin D3 Levels Are Associated With Breslow Thickness at Presentation and Survival From Melanoma. Journal of Clinical Oncology, 2009 Sep 21. [Epub ahead of print]
3. Moan T, et al. Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure, Proceedings of the National Academy of Sciences, 2008; 105(2): 668–673
Dr. John Briffa is a London-based physician and health writer with an interest in nutrition and natural medicine. His Web site is drbriffa.com