Known as the “sunshine vitamin,” vitamin D has been shown to improve bone, thyroid, and kidney health by regulating calcium and phosphate levels in the body.
Recent studies also suggest adequate or above-average levels of vitamin D may help prevent or slow the development of some cancers, but more evidence is needed to confirm these findings.
“We have a lot of interest in vitamins and supplements and how they relate to cancer,” said Therese Bevers, M.D., a professor in the Department of Clinical Cancer Prevention and the medical director of the Cancer Prevention Center at The University of Texas MD Anderson Cancer Center. “Currently, there are very limited data—especially high-level data—that can guide clinical recommendations. But there is some evidence that suggests certain vitamins or supplements may be beneficial in reducing the risk of developing cancer, and one of these is vitamin D.”
How the body processes vitamin D
When exposed to ultraviolet light from the sun, the human body produces vitamin D. The liver then converts vitamin D into 25-hydroxyvitamin D, also called 25(OH)D, which travels through the bloodstream to the kidneys, where it becomes the active form of vitamin D that can be used by the body.
Although sunlight exposure increases the risk of skin cancer, the vitamin D that results from such exposure may reduce the risk of other cancers. Research in the 1980s showed that the rate of developing or dying of certain cancers was lower among people living in southern parts of the United States than in those living in the north, where there is less sunlight.
In addition to sunlight exposure, people can get vitamin D by eating fatty fish, such as salmon and tuna, as well as fortified milk and cereals. For people who live in less sunny climates or do not eat fish, vitamin D supplements are the most convenient option.
Studies have indicated that vitamin D supplements may decrease a person’s risk of breast, colorectal, pancreatic, and prostate cancers. However, these studies were not conclusive. And in a study done this year at the University of California, San Diego, School of Medicine, the participants (all women) who had high levels of vitamin D in their blood had a 67% lower cancer risk compared with women whose vitamin D levels were lower, suggesting that higher vitamin D levels decrease the risk of developing cancer.
In another recent study, researchers at Stanford University School of Medicine found that breast tumors grew faster and spread to more parts of the body in mice with low vitamin D levels than in mice with adequate levels. Dr. Bevers said that this finding suggests that vitamin D may have properties that can slow or prevent the development of cancer, but she added that what happens in a mouse does not necessarily happen in a human.
According to Dr. Bevers, a link between cancer and vitamin D has not been proven in clinical trials. In fact, it is difficult for clinical trials to determine the effect of vitamin D supplements on cancer risk because a person’s diet and the amount of time spent in the sun also affect that person’s vitamin D level.
Getting enough vitamin D
Most experts recommend a daily vitamin D intake of 400 international units (IU) for children younger than 1 year, 600 IU for people 1–70 years old, and 800 IU for those older than 70 years. However, these daily allowances were based on the vitamin’s effect on bone health rather than its potential for cancer prevention.
“At this time, we do not make any recommendations regarding vitamin supplements for cancer prevention,” Dr. Bevers said. “That’s not to say there isn’t ongoing research, but we need to have more conclusive evidence before making those recommendations.”
– Z. Ahmed
For more information, ask your physician, visit www.mdanderson.org or call askMDAnderson at 877-632-6789.
OncoLog, October 2016, Volume 61, Issue 10