While we wait for randomized controlled trials to see if vitamin D supplements reduce the risk of cancer, it is important to occasionally review what the test tube and animal studies show. Recently, Dr Kun-Chun Chiang of the College of Medicine at Chang Gung University in Taiwan teamed up with Professor Tai C. Chen of Boston University School of Medicine to review the mechanisms by which vitamin D prevents and fights cancer in animals and in the test tube.
It is important to remember that Professor Joan Lappe and colleagues published the only randomized controlled trial using meaningful doses of vitamin D in cancer back in 2007. They found vitamin D and calcium together significantly reduced the risk of getting internal cancers.
If Dr Lappe’s findings are verified, and only time and more studies will tell, it is important to realize that thousands of basic science and animal studies have demonstrated that vitamin D has pronounced anti-cancer effects. According to Dr Chiang, vitamin D’s anti-cancer effects involve the following six mechanisms:
- Via four separate mechanisms, vitamin D prevents cellular proliferation. Cancers proliferate by increasing the number of cells via cell growth and cell division.
- Vitamin D promotes apoptosis or programmed cell-death, which is a regulated process that is fundamental to the advantage of the organism. Damaged and old cells must die and be replaced by new cells. Activation of apoptotic pathways is a key mechanism by which chemotherapy helps eliminate tumor cells.
- Vitamin D helps prevent angiogenesis or new blood vessel formation. Pathological angiogenesis can last for years, and is necessary for tumors and their metastases to grow beyond microscopic size.
- Vitamin D promotes cellular differentiation, or cell specialization. Undifferentiated cancers tend to be the most lethal.
- Vitamin D prevents inflammation, and inflammation often leads to cancerous changes in tissues.
- Gene array profiling studies have demonstrated that vitamin D increases the expression of DNA repair genes, suggesting involvement in DNA repair pathways.
As far as we know, these anti-cancer effects of vitamin D are dose dependent up to a certain level. That is, the lower your vitamin D levels are below the ideal level, the less active these anti-cancer mechanisms are. However, no one knows what ideal levels are: the blood levels of vitamin D that are most effective in reducing the risk of cancer. While we wait to find out what ideal levels are, it seems wise to keep natural vitamin D levels: levels found in people living in equatorial regions who wear little clothing. Such levels are around 50 ng/ml, and it takes approximately 5,000 IU/day to achieve in most people.