Relevance of vitamin D in bone and muscle health of cancer patients.

Cancer patients with advanced disease frequently feel weak and fatigued, and have an increased risk of fracture. At the same time several reports describe the high prevalence of vitamin D deficiency in these patients. This review will summarize the impact of vitamin D deficiency on muscle weakness and fracture risk. While larger clinical trials of vitamin D supplementation are lacking in cancer patients, the evidence from clinical trials among older adults of the general population support a significant benefit of vitamin D on muscle strength, and fall and fracture reduction. Mechanistic evidence regarding the presence of the specific vitamin D receptor in muscle tissue and muscle biopsy abnormalities observed with deficiency will be reviewed, as well as molecular and non-molecular effects of vitamin D in muscle tissue. At the clinical level, the evidence from randomized controlled trials of vitamin D supplementation on functional improvement and fall reduction will be summarized. Finally, trial and epidemiological data will be reviewed to assess desirable serum 25-hydroxyvitamin D levels for optimal muscle health.