High prevalence of vitamin D deficiency despite supplementation in premenopausal women with breast cancer undergoing adjuvant chemotherapy

Purpose: Vitamin D deficiency is associated with increased breast cancer risk and decreased breast cancer survival. The purpose of this study was to determine the prevalence of vitamin D deficiency, as measured by serum 25-hydroxyvitamin D (25-OHD), in premenopausal women at initiation of adjuvant chemotherapy for breast cancer and after 1 year of vitamin D supplementation. Patients and Methods: The study included 103 premenopausal women from the northeastern United States with stages I to III breast cancer who received adjuvant chemotherapy and participated in a 1-year zoledronate intervention trial. All patients were prescribed vitamin D3 (cholecalciferol) 400 IU and calcium carbonate 1,000 mg daily. At baseline and at 6 and 12 months, bone mineral density (BMD) measurements were obtained and blood was collected and analyzed in batches for serum 25-OHD. Vitamin D deficiency was defined as serum 25-OHD less than 20 ng/mL, insufficiency as 20 to 29 ng/mL, and sufficiency as 30 ng/mL or greater. Results: At baseline, 74% of women were vitamin D deficient (median, 17 ng/mL). Vitamin D deficiency was slightly less common in white women (66%) compared with black (80%) and Hispanic (84%) women. After vitamin D supplementation for 1 year, less than 15% of white and Hispanic women, and no black women, achieved sufficient 25-OHD levels. Vitamin D levels did not correlate with baseline BMD and were not altered by chemotherapy or bisphosphonate use. Conclusion: Vitamin D deficiency is highly prevalent in women with breast cancer. The current recommended dietary allowance of vitamin D is too low to increase serum 25-OHD greater than 30 ng/mL. Optimal dosing for bone health and, possibly, improved survival has yet to be determined.