Breast cancer survival and recurrence rates are strongly correlated with Vitamin D Deficiency. 

Mean age was 50.4 years, mean vitamin D was 58.1 ± 23.4 nmol/L. Vitamin D levels were deficient (< 50 nmol/L) in 37.5% of patients, insufficient (50 to 72 nmol/L) in 38.5% of patients, and sufficient (> 72 nmol/L) in 24.0% of patients. There was little variation in mean vitamin D levels between summer and winter months. Mean follow-up was 11.6 years; 116 women had distant recurrences, and 106 women died. Women with deficient vitamin D levels had an increased risk of distant recurrence (hazard ratio [HR] = 1.94; 95% CI, 1.16 to 3.25) and death (HR = 1.73; 95% CI, 1.05 to 2.86) compared with those with sufficient levels. The association remained after individual adjustment for key tumor and treatment related factors but was attenuated in multivariate analyses (HR = 1.60; 95% CI, 0.96 to 2.64 for death). 

Pritchard, K.I., Koo, J., Hood, N. Prognostic effects of 25-hydroxyvitamin D levels in early breast cancer. Journal of Clinical Oncology 2009