Vitamin D levels during and after high-dose vitamin D supplementation in women with early-stage breast cancer

Abstract

e20561 Background: Experts define vitamin D deficiency as a 25-hydroxyvitamin D (25OHD) level of < 20 ng/ml; a level < 32 ng/ml is considered insufficient for bone health and > 40 ng/ml may be associated with optimum musculoskeletal function and reduced risk for breast cancer. We conducted a study to determine the effect of high dose vitamin D3 at 50,000 IU/wk (HD vitD) on musculoskeletal symptoms from adjuvant letrozole in breast cancer patients. We present here the effectiveness of HD vitD in achieving optimum 25OHD levels and the rate of decline of 25OHD levels after 12 weeks of HD vitD. Methods: The cohort included post-menopausal women with early stage hormone receptor positive breast cancer initiating letrozole treatment. Women with baseline 25OHD levels < 40 ng/ml received 12 weeks of HD vitD. 25OHD levels were assessed at 6 and 12 weeks during HD vitD supplementation and at 3 and 6 months after completing HD vitD but while taking maintenance dose of 600–1000 IU of vitamin D3 daily. Results: 40 women that received HD vitD completed the follow-up phase of the study and are included in this analysis. At entry on study, median 25OHD level was 23 ng/ml; 38% of the women had vitD deficiency, 75% had insufficiency, and 93% had 25OHD levels < 40 ng/ml. Six weeks of HD vitD increased median 25OHD level to 60 ng/ml and another 6 weeks increased it further to 66 ng/ml. With only 6 weeks of HD vitD supplementation, 98% of the women achieved a 25OHD level of > 40 ng/ml. Median 25OHD levels 3 and 6 months after completion of HD vitD were 49 and 40 ng/ml, respectively. The median rate of decrease in vitD levels per month was 6.8% of the level at completion of supplementation. Using linear regression analysis, projected changes in 25OHD levels were calculated for each subject. Median extrapolated time to drop to a 25OHD level of < 40 ng/ml was 6.0 months, to <32 ng/ml was 7.8 months, and to <20 ng /ml was 10.6 months. Conclusions: Supplementation with vitD3 at 50,000 IU/week for 6 weeks is sufficient to achieve a 25OHD level of >40 ng/ml in 98% of postmenopausal women with breast cancer on an AI. After 12 weeks of HD vitD, there is a steady decline in 25OHD levels at a rate of about 7% per month despite continuing on 600 to 1000 IU of D3 daily. Thus, standard doses of D3 are not adequate to maintain 25OHD levels achieved by HD vitD. No significant financial relationships to disclose.