Vitamin D and Cancer
Vitamin D is essential for the formation, growth, and repair of bones and for normal calcium absorption and immune function. It is obtained primarily through exposure of the skin to ultraviolet radiation in sunlight, but it can also be obtained from some foods and dietary supplements. Some recent research suggests vitamin D may be able to stop or prevent cancer. Now, a new study finds an enzyme that plays a role in metabolizing vitamin D can predict lung cancer survival. The study, from researchers at the University of Michigan Comprehensive Cancer Center, suggests that this enzyme stops the anti-cancer effects of vitamin D. Levels of the enzyme, called CYP24A1, were elevated as much as 50 times in lung adenocarcinoma compared with normal lung tissue. The higher the level of CYP24A1, the more likely tumors were to be aggressive. About a third of lung cancer patients had high levels of the enzyme. After five years, those patients had nearly half the survival rate as patients with low levels of the enzyme.
Vitamin D is technically not a vitamin. It is the name given to a group of fat-soluble prohormones (substances that are precursors to hormones that usually have little hormonal activity by themselves). Two major forms of vitamin D that are important to humans are vitamin D2, or ergocalciferol, and vitamin D3, or cholecalciferol.
Vitamin D2 is made naturally by plants, and vitamin D3 is made naturally by the body when the skin is exposed to ultraviolet radiation (in particular, UVB radiation) in sunlight. Vitamin D2 and vitamin D3 can also be commercially manufactured.
A large number of scientific studies have investigated a possible role for vitamin D in cancer prevention.
The first results came from epidemiologic studies known as geographic correlation studies. In these studies, an inverse relationship was found between sunlight exposure levels in a given geographic area and the rates of incidence and death for certain cancers in that area. Individuals living in southern latitudes were found to have lower rates of incidence and death for these cancers than those living at northern latitudes. Because sunlight/UV exposure is necessary for the production of vitamin D3, researchers hypothesized that variation in vitamin D levels accounted for the observed relationships.
Evidence of a possible cancer-protective role for vitamin D has also been found in laboratory studies of the effect of vitamin D treatment on cancer cells in culture.
Randomized clinical trials designed to investigate the effects of vitamin D intake on bone health have suggested that higher vitamin D intakes may reduce the risk of cancer.
The new research has linked cancer risk reduction to how CYP24A1 interacts with calcitriol, the active form of vitamin D. CYP24A1 breaks down calcitriol, which has a normal and crucial role when kept in check. But when levels of CYP24A1 climb, the enzyme begins to hinder the positive anti-cancer effects of vitamin D.
Results of the study appear in Clinical Cancer Research.
"Half of lung cancers will recur after surgery, so it's important to find a way to prevent or delay this recurrence. A natural compound like vitamin D is attractive because it has few side effects, but it's even better if we can determine exactly who would benefit from receiving vitamin D," says study author Nithya Ramnath, M.D., associate professor of internal medicine at the U-M Medical School.
Current recommendations call for 600-800 IU (international units) of vitamin D daily, depending on age. Studies looking at vitamin D in lung cancer are testing medically administered doses 200 times what could be taken by mouth naturally. Taking large amounts of vitamin D supplements is not currently recommended to prevent or treat lung cancer.
For further information: http://www.eurekalert.org/pub_releases/2011-03/uomh-slv030111.php