  The link appears to be vitamin D specific (at least for colorectal cancer), as shown by PMID 17296473. I have seen some papers discussing the theory behind the link, but I haven't really looked into it in much detail. Maybe someone else can comment on this.  But if large epidemilogical studies are showing that vitamin D/sunlight is a factor in reducing cancer risk, is this not enough to at least mention it? Do we know the exact biological mechanism behind the other cancer risks? My contribution (which was removed by jfdwolff) was just a short paragraph summary taken from a recent review, and I think it is appropriate to put it back in.  