UCL research team offer advice contrary to official medical bodies in Uk concerning Vit D supplements. Doesnt say D3 exactly but I presume they are referring to that rather than the synthetic D2 which isnt so hot.
http://news.bbc.co.uk/1/hi/health/10486310.stm
http://news.bbc.co.uk/1/hi/health/10486310.stm