Madden JM, et al. - In a large national breast cancer cohort, researchers examined the link between vitamin D supplementation started following a diagnosis of breast cancer and related mortality using pharmacy claims data. The National Cancer Registry Ireland database (n = 5,417) was used to identify women aged 50–80 years with a record of invasive breast cancer. Using linked national prescription data, initiation of de novo vitamin D post-diagnosis was identified. Reduced breast cancer-specific mortality was observed in relation to de novo vitamin D use post-diagnosis. Hence, vitamin D has the potential as a non-toxic and inexpensive agent to improve survival in breast cancer patients. A 20% reduction in breast cancer-specific mortality in de novo vitamin D users vs non-users was seen in this study, and the reduction increased to 49% if vitamin D was introduced within 6 months of breast cancer diagnosis.