Vitamin D has long been a friend to men, women and children. Obtained primarily through exposure of the skin to sunlight but also procured in certain foods and dietary supplements, vitamin D helps the body use calcium and phosphorous to improve bone health and build healthy teeth.
But as valuable as vitamin D can be to your bones and teeth, it also may play a role in reducing your risk for certain cancers. The National Cancer Institute notes that many studies have suggested that higher intake of vitamin D or higher levels of vitamin D in the blood are associated with a reduced risk of colorectal cancer. To understand this relationship, it helps to first understand vitamin D.
What is vitamin D?
A group of fat-soluble prohormones, vitamin D comes in two forms that are important to humans. Vitamin D2, also known as ergocalciferol, is made naturally by plants, while vitamin D3 is produced naturally by the body when it is exposed to ultraviolet radiation in sunlight.
How are vitamin D levels in the body measured?
When vitamins D2 and D3 enter the body, they are converted to 25-hydroxyvitamin D in the liver before traveling through the blood to the kidneys, where the 25-hydroxyvitamin D is modified to calcitrol, which is the active form of vitamin D in the body. When a person has their vitamin D levels measured, the most accurate method of doing so is to determine the amount of 25-hydroxyvitamin D in their blood.
How do I get enough vitamin D?
The NCI notes that most people already get at least some of the vitamin D they need through sunlight exposure. In addition to sunlight exposure, many people get plenty of vitamin D from their diets, including foods such as fatty fish, fish liver oil and eggs that naturally contain vitamin D. But foods fortified with vitamin D, such as milk, juices and breakfast cereals, also ensure many people get adequate amounts of vitamin D. For many people, the combination of exposure to sunlight and diet is enough to produce strong bones and healthy teeth and reduce risk for colorectal cancer.
But people who are diagnosed with low levels of vitamin D can look to supplements to ensure they're getting enough. Recommended daily intake guidelines vary depending on age, but those interested in learning these guidelines can find them on the Institute of Medicine website at www.iom.edu.
Why study the connection between vitamin D and cancer?
While studies have previously linked higher levels of vitamin D with reduced risk of colorectal cancer, research is ongoing to determine if vitamin D plays a role in lowering a person's risk of developing other types of cancers as well. Driving this research are early studies that discovered incidence and death rates for certain cancers were lower among people living in southern latitudes than those living in northern latitudes. That's a significant distinction, as levels of sunlight exposure, which is a chief source of vitamin D, are relatively high in southern latitudes and considerably higher in such areas than in northern latitudes. Studies are ongoing into this particular link and if vitamin D is, in fact, behind the lower cancer incidence and death rates.
Another reason to study the connection is that experimental studies conducted on cancer cells and tumors in mice found that vitamin D may play a role in slowing or preventing the development of cancer.
Does vitamin D definitively lower risk for certain cancers?
Though evidence has suggested a link between high vitamin D intake and lower risk of specific cancers, the NCInotes that, thus far, studies have been inconsistent. While numerous studies have concluded that vitamin D reduces a person's risk for colorectal cancer, even that widely acknowledged link remains open to debate. For example, a 2006 study published in the New England Journal of Medicine found that healthy women who took vitamin D and calcium supplements for an average of seven years did not have a reduced incidence of colorectal cancer, though some scientists questioned if that study was extensive enough to support its ultimate conclusion.
More information about the relationship between vitamin D and cancer is available at www.cancer.gov.