This study investigated the association of Vitamin D with tumor characteristics in pre and postmenopausal women.
A prospective cohort of 476 women with incident stage I-III breast cancer (BC) in Alberta, Canada comprised the study population. Vitamin D was measured as 25(OH)D concentration in serum samples collected at diagnosis (presurgery and prior to treatment initiation). Tumor characteristics including size, grade, receptor status, stage and nodal status were evaluated in regression models for association with Vitamin D and measured cytokines in models adjusted for menopausal status.
More than half of the women were diagnosed as stage I and Luminal A/B, most were postmenopausal, had sufficient Vitamin D levels, and were 56.6 years of age on average. Higher vitamin D levels were associated with decreased tumor size for all women with larger effect seen in premenopausal status. Insufficient vitamin D levels were significantly associated with increased risk of higher grade, but only in premenopausal women. Elevated human granulocyte macrophage colony-stimulating factor was an independent risk factor associated with increased risk of higher-grade tumors.
Women with sufficient Vitamin D levels at BC diagnosis had smaller and lower grade tumors compared to women with insufficient vitamin D, especially among premenopausal women. Maintaining adequate vitamin D levels in premenopausal women could improve prognostically important BC characteristics at diagnosis.

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