Higher vitamin D levels at time of breast cancer diagnosis may correlate to positive overall survival when compared to women with lower serum levels of vitamin D. The finding comes from the latest analysis of the Pathway Study, an ongoing prospective cohort study of  women with a diagnosis of invasive breast cancer.

The study cohort was established in Kaiser Permanente in California n 2006 with enrollment completed in 2013. Women with incident invasive breast cancer typically consented and enrolled within 2 months of diagnosis; overall enrollment rate was 46% (4,505 of 9,820). Participants are followed after a baseline interview for outcomes and comorbidities at 12, 24, 48 72 and 96 months. The case-cohort design was used for efficiency assay of 25-hydroxyvitamin D (25OHD) among the selected 1,666 cohort members with serum samples.

The primary outcomes of the study include breast cancer recurrence, second primary cancer, and death. Results showed that women with the highest tertile of 25OHD measures had a superior overall survival (OS) compared to women in the lowest tertile. The relationship remained even after adjusting for clinical prognostic factors (hazard ratio 0.72; 95% CI: 0.54-0.98).  

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Serum 25OHD concentrations were lower in women with advanced-stage tumors, and the lowest in premenopausal women with triple-negative cancer.

Overall survival was strongest among premenopausal women in the highest 25OHD tertile group (OS: HR 0.45, 95% CI: 0.21-0.96). Additionally this group was also associated with stronger breast cancer-specific survival (HR 0.37, 95% CI, 0.15-0.93) and invasive disease-free survival (HR 0.58; 95% CI: 0.34-1.01).

The authors concluded that their findings present, “compelling observational evidence on associations of vitamin D with lower risk of breast cancer morbidity and mortality.”

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