Background Vitamin D deficiency is common and can be associated with multiple symptoms including fatigue and pain. These symptoms are common in advanced cancer, and the prevalence of vitamin D deficiency in adults with advanced cancer has been estimated at 47–90%. The aim is to systematically review the available evidence for the supplementation of vitamin D for adults with advanced cancer, to assess the impact on pain, fatigue and quality of life.

Methods An electronic search (PubMed, clinical trial databases) was undertaken in October 2017, using search terms ‘Vitamin D’ and ‘cancer’, filtered for clinical trials. This was supplemented by a search of palliative and oncological journals.

Inclusion criteria:

• Population- adults with advanced/metastatic cancer;

• Intervention- systemic vitamin D, any dose;

• Comparison- placebo or other;

• Outcomes- quality of life, pain or fatigue.

Exclusion criteria:

Conference abstracts; studies in which the effect of vitamin D could not be distinguished from another agent, because given with e.g. chemotherapy.

Results Electronic searches yielded 419 titles and abstracts (PubMed), 449 titles (journal search), 110 registered studies (trial databases), including duplicates. Of these, 79 articles were reviewed in detail. No completed randomised controlled trials were identified. One case-control study (retrospective controls) and four single-arm studies were identified. Four of these studies reported an improvement in symptoms or reduction in opioid dose, suggesting that vitamin D supplementation may have a role in symptom relief for people with advanced cancer, but there is a high risk of bias.

Two double-blind placebo-controlled RCTs (VIDAFACT, Palliative D) are ongoing.

Conclusion There is low quality evidence that vitamin D supplementation may improve pain and weakness in adults with advanced cancer. Two ongoing placebo-controlled RCTs should provide more robust evidence to guide clinical practice. In the meantime it seems reasonable to remain vigilant for vitamin D deficiency, and to recommend supplementation if deficiency appears symptomatic.