It appears that maintaining adequate vitamin D is linked with avoiding cancer.1 While the article primarily looks at breast cancer, it also mentions colon and prostate cancer, and one researcher quoted thinks that it might be true of cancer in general.
Mr. Nigel Hawkes. "Sunshine helps in the fight against breast cancer" Times Online 2007-08-04. http://www.timesonline.co.uk/tol/news/uk/health/article2195614.ece ↩