I've been taking vitamin D3 on my naturopath and therapist's advice. I haven't read anything about its effect specifically on concussion recovery. Nor am I sure how conclusive the research is on the health benefits of D3 - I tend to be skeptical of the latest fads in vitamins and supplements. However, there seems to be some suggestion that it may be helpful for mood / cognition / brain function (see below - random links culled from the web).

http://www.livestrong.com/article/22...its-vitamin-d/

http://www.scientificamerican.com/ar...e-a-difference

http://www.dana.org/news/cerebrum/detail.aspx?id=20980