Vitamin D for the treatment of chronic painful conditions in adults

Cochrane: Chronic pain is pain of moderate or severe intensity lasting three months or more. It can have a variety of causes, but most comes from musculoskeletal conditions such as arthritis, or pain in muscles. Chronic pain usually affects older people more than younger people. Chronic pain is disabling, and has a large negative impact on quality of life. 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 conditions, including chronic pain.

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 low levels of vitamin D and chronic pain has attracted interest because - if it were true - vitamin D would be an inexpensive and relatively safe treatment.
We searched scientific databases for studies comparing vitamin D supplementation with placebo (a dummy treatment) or active medicines for the treatment of chronic painful conditions in adults. The evidence is current to February 2015.
There is a small amount of evidence supporting this link but it is not of high quality and may not be reliable. This update of a review sought high quality evidence from randomised controlled trials (studies where participants are randomly allocated to receive one of several treatments) on vitamin D for chronic painful conditions.
We found no consistent pattern that vitamin D treatment was better than placebo for any chronic painful condition, but the studies had methodological shortcomings (low quality evidence).
More research is needed to determine if vitamin D is a useful pain treatment in any particular chronic painful condition. That research should examine whether any effect is restricted to people who are vitamin D deficient. It should also examine how much vitamin D is required, and for how long, before beneficial effects occur.

Authors' conclusions: 

The evidence addressing the use of vitamin D for chronic pain now contains more than twice as many studies and participants than were included in the original version of this review. Based on this evidence, a large beneficial effect of vitamin D across different chronic painful conditions is unlikely. Whether vitamin D can have beneficial effects in specific chronic painful conditions needs further investigation.