Cochrane reviews not enough high quality RCT for Vitamin D and  chronic pain Feb 2010
Vitamin D for the treatment of chronic painful conditions in adults
http://www.cochrane.org/reviews/en/ab007771.html 
Straube S, Derry S, Moore RA, McQuay HJ
Vitamin D has a variety of roles in the body. It is made in the skin through the action of sunlight and can also be obtained from food. A lack of vitamin D has been implicated in a number of diseases, including chronic painful conditions. Additionally, associations of such diverse types of pain as headache, abdominal pain, knee pain, and back pain with season of the year and latitude provide indirect support for a role for vitamin D. The possibility of a link between vitamin D and chronic pain has attracted interest because - if it was true - vitamin D would be a cheap and relatively safe treatment for chronic pain. There is some evidence supporting this link but it is not of high quality and is at risk of bias. This review sought out high quality evidence from Randomised Controlled Trials on the treatment of chronic pain with vitamin D. There were few high quality studies of which only one reported a beneficial effect. At present, therefore, there is insufficient evidence for an effect of vitamin D in chronic pain conditions. More research is needed to determine if vitamin D is a useful pain treatment at all and if so, whether the effect is restricted to those who are vitamin D deficient, how much vitamin D is useful, in which conditions, and for how long.