Association Between Low Vitamin D Levels and the Greater Impact of Fibromyalgia

Background: Fibromyalgia (FM) is a clinical syndrome mainly characterized by generalized chronic pain, fatigue, sleep and cognition disorders. The role played by vitamin D in the pathophysiology of painful syndromes is poorly known. Studies assessing the association between vitamin D and FM have presented conflicting results. The aims of the current study were to assess vitamin D levels in FM patients, by comparing them to healthy controls, as well as to analyze their impact on this disease.

Methods: This was a cross-sectional study comprising 43 FM patients (ACR 2010 criteria) and 40 healthy individuals. All participants had their vitamin D levels measured, and FM patients also had their total calcium, albumin, phosphorus and parathyroid hormone (PTH) measured. Clinical variables capable of affecting the results were evaluated and the fibromyalgia impact questionnaire (FIQ) was applied.

Results: There was not statistically significant difference in global mean values of vitamin D between groups. In the total sample, only 4.8% of the individuals had vitamin D deficiency, which corresponded to the deficiency found in the group of patients; in the control, no one had vitamin deficiency; 39.8% had insufficient levels and 55.4% with sufficient levels. The mean serum vitamin D values were similar between the FM and control groups (34.8 ± 12 and 34.7 ± 12.3 ng/mL, respectively; P = 0.806). However, a significant negative correlation was found between vitamin D concentration and FIQ values, that is, patients with the greatest impact of the disease had lower concentrations of vitamin D (P = 0.018).

Conclusion: FM patients did not present higher prevalence of vitamin D deficiency or insufficiency than healthy individuals, although low vitamin D concentrations could indicate more severe disease impacts.

Keywords: Chronic pain; Fibromyalgia; Fibromyalgia impact; Vitamin D.