Vitamin D: Cancer Prevention's Sunny Future?
Authors: S. Beres
Journal: JNCI Journal of the National Cancer Institute (2008)

C ould preventing cancer be as easy as taking a vitamin supplement? For decades, studies have suggested that sunlight and vitamin D decrease the risk of some nonskin cancers. In the past few years, there has been a crescendo in the research, including results from the first randomized, controlled trial to show that vitamin D can lower cancer risk. The Canadian Cancer Society thinks that vitamins might be one way to prevent some cancers. In June 2007, the national organization recommended that adults living in Canada consider taking vitamin D supplements of 1,000 international units (IU) a day in the fall and winter. Those at high risk of low vitamin D levels should take it year round. The move was a break from the Canadian government’s daily intake recommendation of 200 – 600 IU, which is aligned with the U.S. Institute of Medicine’s adequate intakes. Then, in October, the Canadian Cancer Society wrote a letter to North American research granting agencies, including the National Institutes of Health, lobbying for a large-scale clinical trial that tests at least 1,000 IU of vitamin D. The goal: to fi gure out what dose prevents cancer. Although making a recommendation and asking for more research at the same time may seem contradictory, Heather Chappell, senior manager of cancer control policy for the Canadian Cancer Society, said that this approach struck a balance between two health issues. One is geographic location — 90% of vitamin D comes from the sun when ultraviolet rays convert a precursor in the skin to vitamin D, but during fall and winter at higher latitudes, no vitamin D synthesis occurs. Findings from a conference on vitamin D and health, sponsored by the cancer society and the National Cancer Institute of Canada, concluded that overall vitamin D levels may be low in the general population and that “vitamin D may have benefi cial effects on some types of cancer.” The other issue is reminding Canadians to protect themselves from the sun. Tanning salons in Canada were advertising indoor tanning as a venue to get your vitamin D, which most scientists consider dangerous because of the skin cancer risk. “Taking a supplement is a safer alternative for Canadians than indoor tanning,” Chappell said. “That recommendation is only based on what we know to date.” What the society does know is based on a combination of the conference fi ndings (which brought together 14 national health organizations) and a review of about 60 studies, mostly o b s e r v a t i o n a l , Chappell said. But making recommendations before there have been many randomized, controlled trials concerns some researchers. Several research conferences and organizations have looked at the many questions that still need to be answered about vitamin D and cancer risk. “When you fi nd something in observational studies, the interventions are rarely, rarely as positive or as powerful as the observations,” said Wake Forest University professor Gary Schwartz , Ph.D., who has been examining the vitamin D link to prostate cancer for two decades. “It is an open question whether vitamin D supplementation will reduce the risk of cancer. The questions are how much vitamin D, when, and what cancer.” Ecologic, epidemiologic, and laboratory studies have provided evidence linking higher vitamin D exposures to lower risk of colon, breast, and prostate cancers. But a U.S. National Cancer Institute conference in May 2007 determined that there are many gaps in the research. The conference was spurred by the “sunshine vitamin” getting a lot of attention in the lay press, for which pace picked up after results from a randomized trial were published.