What's the latest research on the interaction/detrimental effects of vitamin a (eg from raw carrots) on vitamin d3 (from sunlight) effectiveness?

Militant fringe: This is at present a fringe idea, primarily the work of a handful of pro-vitamin-d, anti-vitamin-a militants on anti-doctor websites; the centerpiece is a 2009 number-crunch journal article on vitamin d levels and colon cancer with a tiny sidebar on vitamin a. I hesitate to draw cause-and-effect conclusions from studies based only on statistics without an obvious mechanism.