Prevalence of Vitamin D Deficiency and Its Relationship with Clinical Outcomes in Patients with Fibromyalgia: a Systematic Review of the Literature

Fibromyalgia is a debilitating chronic condition which poses a therapeutic challenge to the clinician. With a large backlog in patient flow subsequent to the COVID-19 pandemic and rising numbers of patients with post-acute sequelae of COVID-19 (PASC) presenting with fibromyalgia-like clinical features, there is an increasingly pressing need to identify broad cost-effective interventions. Low levels of vitamin D have previously been reported in patients with fibromyalgia, though any causative link has been difficult to establish. A systematic literature review on the association between vitamin D deficiency and fibromyalgia was performed examining retrospective evidence both for and against an association between vitamin D deficiency (VDD) and fibromyalgia and evaluating the therapeutic benefit from supplementation. A group of six studies were selected based on relevance, use of controls, quality of research and citations. Four primary studies assessing the prevalence of VDD in fibromyalgia patients versus controls were evaluated with a total 3,496 subjects. Three included females only and one larger study assessed males. Two (n = 313) concluded the presence of a statistically significant association, and two (n = 161) found none. Two randomised controlled trials assessing the effect of vitamin D supplementation in a total of 80 subjects found conflicting results, with pain reduction in one and none in the other. It is likely there exists an association between VDD deficiency and fibromyalgia in a large subset of patients, although establishing primary causation is difficult. There is a need for larger randomised controlled trial designs with more effective comparison with healthy subjects and control for confounding factors. Given VDD is a major problem in the general population, we recommend supplementation be recommended by healthcare professionals to fibromyalgia patients for the purpose of maintaining bone health given their potentially increased susceptibility to developing deficiency and its sequelae.