If you found the Holick lecture above interesting you may also like this paper. It is a bit technical but if you ignore the bits that are complex you will get the gist that greater sun exposure may = lower risk of a range of cancers, that most if not all tissues use and can make the active form of vitamin D from the vitamin D precursor made by the action of sunlight in the skin, and that it appears that Vit D helps regulate cell division.
Vitamin D: Its role in cancer prevention and treatment
Michael F. Holick
Prog Biophys Mol Biol. 2006 Sep;92(1):49-59. Epub 2006 Mar 10.
Vitamin D: its role in cancer prevention and treatment.
Holick MF.
Source
Boston University Medical Center, 715 Albany Street, M-1013, Boston, MA 02118, USA.
mfholick@bu.edu
Abstract
Vitamin D, the sunshine vitamin, has been recognized for almost 100 years as being essential for bone health. Vitamin D provides an adequate amount of calcium and phosphorus for the normal development and mineralization of a healthy skeleton. Vitamin D made in the skin or ingested in the diet, however, is biologically inactive and requires obligate hydroxylations first in the liver to 25-hydroxyvitamin D, and then in the kidney to 1,25-dihydroxyvitamin D. 25-Hydroxyvitamin D is the major circulating form of vitamin D that is the best indicator of vitamin D status. 1,25-dihydroxyvitamin D is the biologically active form of vitamin D. This lipid-soluble hormone interacts with its specific nuclear receptor in the intestine and bone to regulate calcium metabolism. It is now recognized that the vitamin D receptor is also present in most tissues and cells in the body. 1,25-dihydroxyvitamin D, by interacting with its receptor in non-calcemic tissues, is able to elicit a wide variety of biologic responses. 1,25-dihydroxyvitamin D regulates cellular growth and influences the modulation of the immune system. There is compelling epidemiologic observations that suggest that living at higher latitudes is associated with increased risk of many common deadly cancers. Both prospective and retrospective studies help support the concept that it is vitamin D deficiency that is the driving force for increased risk of common cancers in people living at higher latitudes. Most tissues and cells not only have a vitamin D receptor, but also have the ability to make 1,25-dihydroxyvitamin D. It has been suggested that increasing vitamin D intake or sun exposure increases circulating concentrations of 25-hydroxyvitamin D, which in turn, is metabolized to 1,25-dihydroxyvitamin D(3) in prostate, colon, breast, etc. The local cellular production of 1,25-dihydroxyvitamin D acts in an autocrine fashion to regulate cell growth and decrease the risk of the cells becoming malignant. Therefore, measurement of 25-hydroxyvitamin D is important not only to monitor vitamin D status for bone health, but also for cancer prevention.