A January 2010 article in the British Medical Journal looked at large population samples from Western Europe and found that higher Vitamin D levels were associated with a substantial reduction in risk of colorectal cancer.
Many public health advocates are now suggesting that supplementation in the range of 1,800 to 4,000 IU vitamin D per day may provide multiple benefits, including reduction in risk of some cancers.
Reference: Jenab, M, et al. Association between pre-diagnostic circulating vitamin D concentration and risk of colorectal cancer in European populations: a nested case-control study.
British Medical Journal, 21 January 2010.