Vitamin D and Chronic Low Back Pain
Chronic non-specific low back pain is one of the most common presentations in primary care. Vitamin D deficiency causes a soft-bone condition (osteomalacia) that can mimic musculoskeletal back pain — deep, diffuse, worse with bearing weight, and often accompanied by proximal muscle weakness. Undiagnosed deficiency is a correctable cause worth screening for.
The Al Faraj study
A landmark 2003 Saudi Arabian study (Al Faraj) of 360 adults with chronic low back pain found 83% had 25(OH)D deficiency. Supplementation with cholecalciferol 5,000–10,000 IU/day for 3 months resulted in clinical improvement in 95% of patients. This study has been criticised for lack of blinding and control, but the magnitude and the mechanism are consistent with osteomalacia.
Subsequent trial evidence
- Sandoughi 2015 — 53 deficient patients; 50,000 IU weekly × 8 weeks reduced pain intensity and functional disability vs placebo.
- Ghai 2017 (India) — 68 patients; 60,000 IU weekly × 8 weeks improved VAS pain and Modified Oswestry Disability Index.
- 2018 meta-analysis of 8 RCTs — significant reduction in pain scores favouring vitamin D, effect largest in patients with baseline 25(OH)D < 20 ng/mL.
- General population trials — no benefit in unselected patients without deficiency.
Osteomalacia — the mechanism
Severe vitamin D deficiency (25(OH)D < 10 ng/mL, usually with elevated PTH and alkaline phosphatase) causes defective bone mineralisation. Trabecular and cortical bone accumulates unmineralised osteoid, which is painful and mechanically weak. Classical presentation: bone pain, proximal myopathy, difficulty rising from a chair. Diagnosis: 25(OH)D, calcium, phosphate, PTH, alkaline phosphatase; imaging may show Looser's zones on X-ray.
Practical approach
- Chronic back pain persisting > 6 weeks: test 25(OH)D, calcium, and PTH.
- Baseline 25(OH)D < 20 ng/mL: correct with 4,000–5,000 IU/day for 8–12 weeks or 50,000 IU/week × 8 weeks; expect improvement over 6–12 weeks.
- Baseline > 30 ng/mL: vitamin D unlikely to be your answer; focus on physical therapy, movement, and appropriate imaging if red flags.
- Vitamin D adjunct does not replace exercise therapy, NSAIDs, or referral for imaging when there are red flags (fever, night pain, neurology, cancer history).