evidence: What is the best source of vitamin D3 -- from lanolin in sheep's wool or from fish oil? [...] In online forums some people allergic to wool have reported allergic reaction to taking vitamin D3, particularly at larger doses. There does not seem to be scientific research on this topic, but, if this is of concern, you can take vitamin D2. It may not be quite as effective as vitamin D3 at raising blood levels, but it can certainly help.