In a prospective study of 16,818 adults, there was an inverse association between vitamin D levels and colorectal cancer mortality. During 6-12 years of follow-up, a serum vitamin D level of 80 nmol/L or higher was associated with a 72% reduced risk of colorectal cancer mortality, compared to vitamin D levels under 50 nmol/L.1
Although this study did not show a decrease in overall cancer deaths associated with vitamin D levels, a sister study showed a 26% lower overall mortality rate for those with higher vitamin D levels.2
1"Prospective Study of Serum Vitamin D and Cancer Mortality in the United States," Freedman DM, Looker AC, et al, J Natl Cancer Inst, 2007 Oct 30; [Epub ahead of print].
2"25-hydroxyvitamin D levels and the risk of mortality in the general population," Arch Intern Med. 2008 Aug 11;168(15):1629-37.