The review - by researchers from the Department of Psychobiology at the Federal University of São Paulo in Brazil - is published in the Journal of Endocrinology.
The researchers explain that while the role of vitamin D in bone metabolism is well established, there is also evidence emerging that it takes part in other biological processes, such as processing of sensory signals and sleep regulation.
Another link that is well established is that which ties pain to sleep disturbance. What is not clear, however, is how vitamin D fits into this relationship.
In their review, the researchers look at recent studies that examine the links between vitamin D, sleep, and pain. They also suggest that health professionals should consider these associations when recommending treatments for patients with all types of pain condition, including chronic back pain, fibromyalgia, arthritis, and menstrual cramps.
Senior author Dr. Monica Levy Andersen says, "We can hypothesize that suitable vitamin D supplementation combined with sleep hygiene may optimize the therapeutic management of pain-related diseases, such as fibromyalgia."
She emphasizes the importance of understanding the mechanisms that link sleep, vitamin D, and pain - such as the immunological and neurobiological pathways.
The management of pain is a complex area of medicine that spans a vast range of research and treatments. Pain affects more people in the United States than heart disease, cancer, and diabetes combined.
Pain is the most common reason for U.S. individuals to access the healthcare system, and it accounts for a large proportion of the country's healthcare costs.
Two ways that vitamin D influences pain sensitivity
In their article, the researchers classified pain into three main types: nociceptive (arising from injury or damage to tissue and detected by sensory neurons); neuropathic (arising from disease or injury of the nervous system); and pain that has an emotional origin.
They explain how pain is regulated by both the central nervous system (the brain and spinal cord) and the peripheral nervous system (which includes the part that picks up signals from sensory neurons and relays them to the brain and spinal cord).
They also describe how interaction between the immune system and the peripheral nervous system - for instance, in inflammation - can increase pain sensitivity (known as hyperalgesia).
New research also shows that there two ways in which vitamin D can affect pain sensitivity: one is through its influence on sleep, and the other is through its influence on inflammation.
In their paper, the researchers highlight the 19 "most relevant" studies (published between 2011 and 2017) that examined the role of vitamin D in sleep disturbance. The studies either explored conditions such as restless legs syndrome, obstructive sleep apnea, and narcolepsy, or used more general measures such as sleep quality and sleep duration.
They also highlight another 16 studies (published between 2008 and 2017) that they note as most relevant to the examination of the link between vitamin D and chronic pain conditions. The conditions they covered included: musculoskeletal pain, fibromyalgia, rheumatoid arthritis, sickle cell disease, cancer, and low back pain.
Working hypothesis for further research
Following their review, the authors propose a working hypothesis for further research. This suggests that "chronic pain and sleep disorders share a bidirectional relationship, in which vitamin D deficiency may play an important role."
The hypothesis proposes that vitamin D - in its biologically active form - works by stimulating the anti-inflammatory response produced by immune cells. This reduces pain sensitivity, which, in turn, improves sleep quality.
Therefore, the authors suggest that vitamin D supplements - together with good sleep hygiene - could improve the effectiveness of pain management approaches used to treat a range of conditions.
This could be a simple yet effective means of improving quality of life for patients and reducing the burden on healthcare, they note.
In his capacity as journal editor, Sof Andrikopoulos, an assistant professor at the University of Melbourne in Australia, comments on the importance of the findings, which he describes as "very exciting and novel". He adds:
"We are unraveling the possible mechanisms of how vitamin D is involved in many complex processes, including what this review shows - that a good night's sleep and normal levels of vitamin D could be an effective way to manage pain."