A recent prospective cohort study published in Pain Medicine suggests that low vitamin D levels heightens pain sensitivity.
Past research has shown that low levels of vitamin D may be associated with pain in various conditions.
For example, a previous study in osteoarthritis patients found low levels of vitamin D to be related to increased mechanical pain sensitivity but not to self-reported clinical pain. Mechanical pain is pain that occurs when there is physical injury to tissue, while self-reported clinical pain is pain that is caused by a chronic condition or disease that does not cause physical damage to tissues and is reported by patients to their physician.
Based upon this finding, researchers from Bern University Hospital and University of Bern in Switzerland conducted a study to determine if low vitamin D levels in a sample of patients with chronic pain disorders may relate to the central processing of mechanical pain. Central processing of pain is the process by which the brain interprets signals from pain receptors throughout the body. Since vitamin D has anti-inflammatory properties, the researchers proposed that low vitamin D levels may increase inflammation in the limbic system, and consequently, increase sensitivity to mechanical pain.
The researchers enrolled 174 patients with chronic pain disorders with or without an explained medical cause at the beginning of the disease. The patients’ vitamin D levels were tested shortly after hospital referral.
To measure the central processing of mechanical sensitivity, a clamp was placed on the nail bed of the middle fingers of the participants for 10 seconds. Patients then reported their pain on a scale ranging from 0 (“no pain”) to 10 (“the most intense pain imaginable”). The test was performed on the middle finger of each hand to account for side-specific differences in pain perception, and the average score from both fingers was used for analysis.
Here were the results:
- 71% of the patients had vitamin D deficiency (<20 ng/ml), 21% had vitamin D insufficiency (20 ng/ml- 30 ng/ml), and 8% were sufficient in vitamin D (>30 ng/ml).
- Lower vitamin D levels were significantly associated with higher pain sensitivity scores (p= 0.011).
- Each decrease of 10 ng/ml in vitamin D levels were related to a .607 unit increase in pain sensitivity scores.
The researchers concluded,
“We found a significant inverse association between continuously scaled 25-OH D levels and mechanical pain sensitivity. This finding is in agreement with experimental animal work on provoked pain sensitivity.”
They went on to admit some limitations of the study:
“The cross-sectional and nonexperimental design preclude any causal and mechanistic inferences. Theoretically, low [vitamin D] levels might contribute to increased central hypersensitivity of multiple organ systems or, alternatively, central processes could inhibit vitamin D metabolism top down.”
They also realized that a lack of information on the source of the vitamin D in the patients could have impacted their findings.
Future studies should utilize a control group to assess whether the association between vitamin D levels and increased pain sensitivity is specific to chronic pain patients.