Clinically Sufficient Vitamin D Levels With Survival and Cardiovascular Outcomes in a Prospective Cohort of 3,995 Individuals Diagnosed With Invasive Breast Cancer.

[BACKGROUND] Vitamin D deficiency is prevalent in patients with breast cancer. The existing body of literature links vitamin D to lower total cancer mortality, yet the evidence on cardiovascular health is mixed. As there have been no randomized clinical trials on vitamin D supplementation in patients with breast cancer, evidence from large prospective studies is valuable to inform recommendations for this patient population.

[PATIENTS AND METHODS] We measured serum 25-hydroxyvitamin D (25OHD) levels in 3,995 women with incident breast cancer in a prospective cohort, which were categorized based on clinical cut points and evaluated with cancer survival outcomes and incident cardiovascular events.

[RESULTS] The median follow-up was 12.2 (range, 0.2-16.3) years. Patients with sufficient versus deficient vitamin D levels had better overall survival (adjusted hazards ratio [HR], 0.76; 95% CI, 0.62-0.93; P for trend =.005), second primary cancer-free survival (HR, 0.75; 95% CI, 0.63-0.90; P for trend =.003), and disease-free survival (HR, 0.82; 95% CI, 0.70-0.97; P for trend =.05). The associations were stronger in patients with stage ≥II disease (P for interaction <.05). Sufficient vitamin D levels were also associated with lower risk of any incident cardiometabolic risk factors (subdistribution HR [sHR], 0.67; 95% CI, 0.54-0.83; P for trend <.001), diabetes, and dyslipidemia, with suggestive lower hazards of cardiovascular disease (CVD), but not CVD-related death (sHR, 0.74; 95% CI, 0.47-1.15; P for trend =.19).

[CONCLUSIONS] Our study provides strong evidence supporting the association between vitamin D sufficiency and both improved cancer survival outcomes and cardiometabolic benefits in women following a breast cancer diagnosis. It may be advisable to routinely screen for vitamin D deficiency in this patient population and treat it when clinically indicated through daily vitamin D supplementation to improve cancer prognosis and cardiometabolic health.