Vitamin D and Fibromyalgia
A significant fraction of patients presenting with fibromyalgia-like diffuse musculoskeletal pain turn out to have vitamin D deficiency — sometimes severely so. Correcting deficiency doesn't cure fibromyalgia, but it does resolve a common confounding cause of aching pain and can meaningfully improve symptom burden in those genuinely deficient.
Osteomalacia mimics fibromyalgia
Sub-clinical osteomalacia — inadequate bone mineralisation from prolonged vitamin D deficiency — presents with the exact pattern that leads to a fibromyalgia diagnosis: diffuse muscle and bone aching, fatigue, and non-restorative sleep. A landmark study (Plotnikoff & Quigley 2003) found 93% of 150 adults presenting with persistent musculoskeletal pain had serum 25(OH)D deficiency, and correction resolved pain in the majority. This alone justifies checking 25(OH)D at any fibromyalgia workup.
Trials in confirmed fibromyalgia
In patients who meet ACR fibromyalgia criteria and are also vitamin D deficient, supplementation to sufficiency reduces pain scores by 20–40% and improves fibromyalgia impact scores in most trials. Effect sizes are smaller in fibromyalgia patients who were sufficient at baseline. The mechanism likely involves both direct effects on muscle function (vitamin D receptors in muscle) and reduced nociceptive sensitisation.
Chronic non-specific pain
Beyond fibromyalgia specifically, meta-analyses of vitamin D for chronic pain of any cause show small-to-moderate pain reduction, again driven by trials in deficient participants. This includes low back pain, arthritis-related pain, and post-surgical chronic pain.
Practical approach
- Test 25(OH)D in any patient with persistent diffuse musculoskeletal pain.
- Correct deficiency aggressively — 6,000 IU/day cholecalciferol for 8 weeks, then 2,000 IU/day maintenance.
- Retest 25(OH)D at 3 months.
- Expect pain improvement to lag repletion by 4–12 weeks.
- If pain persists after 25(OH)D reaches ≥ 40 ng/mL, continue standard fibromyalgia management: graded aerobic exercise, CBT, and if indicated, duloxetine, milnacipran, or pregabalin.