On November 3 at the University of Toronto, Ontario, Canada, noted doctors Cedric Garland and Tracey O’Connor are running a seminar on how vitamin D can be used to prevent breast cancer — as well as infectious diseases, type 1 diabetes, hypertension, colon cancer, and falls in the elderly. http://articles.mercola.com/sites/articles/archive/2009/10/10/Vitamin-D-Experts-Reveal-the-Truth.aspx
There is a video in the previous link that is 29 minutes long but well worth watching. There is a chart shown on the video that you can see from this link http://www.grassrootshealth.net/media/download/disease_incidence_prev_chart_101608.pdf that is astonishing! It shows things like an 83 percent reduction on breast cancer by having double the base line level of vitamin D in your blood! That chart takes a minute to load but is worth it.