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Breast Cancer Res Treat. 2018 Nov;172(1):179-190. doi: 10.1007/s10549-018-4896-6. Epub 2018 Jul 23.

De novo vitamin D supplement use post-diagnosis is associated with breast cancer survival.

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Population Health Sciences Division, Royal College of Surgeons in Ireland, Dublin, Ireland.
Population Health Sciences Division, Royal College of Surgeons in Ireland, Dublin, Ireland.
Department of Public Health and Primary Care, Trinity College Dublin, Dublin, Ireland.



Experimental laboratory data have indicated a protective effect of vitamin D on breast cancer progression, while epidemiological evidence is growing. Using pharmacy claims data, this study investigates the association between vitamin D supplement use initiated after a breast cancer diagnosis and associated mortality.


Women aged 50-80 years with a record of invasive breast cancer were identified on the National Cancer Registry Ireland database (n = 5417). Initiation of de novo vitamin D post-diagnosis was identified from linked national prescription data (n = 2581, 49%). Multivariate Cox proportional hazards models were used to estimate adjusted HRs (95% CIs) for breast cancer-specific mortality.


There was a 20% reduction in breast cancer-specific mortality in de novo vitamin D users (modelled as a time-varying variable) compared to non-users (HR 0.80; 95% CI 0.64-0.99, p = 0.048) and the reduction was greater at 49% (HR 0.51; 95% CI 0.34-0.74, p < 0.001), if vitamin D was initiated soon after the breast cancer diagnosis (within 6 months).


In this large national breast cancer cohort, de novo vitamin D use post-diagnosis was found to be associated with a reduction in breast cancer-specific mortality. Vitamin D, therefore, has the potential as a non-toxic and inexpensive agent to improve survival in breast cancer patients. Findings support the need for RCTs exploring the effect of vitamin D supplementation on breast cancer survival.


Breast cancer mortality; Prognosis; Supplement use; Vitamin D

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