This article is mostly a repeat of whats been posted before but I especially like this one paragraph:
"Our findings of decreased all-cancer risk with improved vitamin D status are consistent with a large and still growing body of epidemiologic and observational data showing that cancer risk, cancer mortality, or both are inversely associated with solar exposure, vitamin D status, or both," write the authors. "These findings highlight the importance of promoting optimum vitamin D status and underscore the value of achieving and maintaining a high serum 25(OH)D concentration."
SOURCE:
http://www.medicalnewstoday.com/articles/78856.php