The results of a phase 2 trial of vitamin D supplementation in women with Stage IV breast cancer have been reported. Vitamin D deficiency has been found to be associated with breast cancer development and progression, and has also been reported in conjunction with increased toxicity from bisphosphonate therapy. Bisphosphonates, which are also used to treat osteoporosis, are used to treat bone metastases in advanced breast cancer patients. The optimal dose of vitamin D supplementation has not been established, however it is possible to obtain the equivalent of a 10,000-IU dose of vitamin D3 from daily sunlight exposure. The study was designed to assess the effect of this dose of vitamin D3 in 40 breast cancer patients with bone metastases who were being treated with bisphosphonates. Participants received daily supplements consisting of 10,000 IU of vitamin D3 and 1000 mg of calcium for four months.

The supplementation regimen was not found to influence bone resorption, nor did it reduce pain overall. However, a reduction in the number of pain sites was observed. Daily doses of 10,000 IU vitamin D3 for four months were found to be safe in patients without conditions causing hypersensitivity to vitamin D. Furthermore, treatment reduced elevated parathyroid hormone levels, which presumably had been caused by long-term bisphosphonate use. However, there did not appear to be a significant palliative benefit nor any significant change in bone resorption.

Vitamin D reduces risk of breast cancer and inhibits progression

The researchers were able to report that supplementation with 10,000 IU of vitamin D daily was generally safe in women with stage IV breast cancer with bone metastases, and that it reduced parathyroid hormone levels that had been increased by bisphosphonate treatment. However, the results with respect to pain relief and bone resorption were no doubt disappointing. While vitamin D deficiency is associated with increased risk of breast cancer, administering vitamin D after breast cancer has progressed to stage IV may be ineffective in slowing disease progression. On the other hand, having established the safety of such as regimen, researchers may be in a position to develop a vitamin D-based treatment that is more effective.