Vitamin D repletion and prevention of bone loss in nonosteoporotic women with breast cancer.

9026 Background: Aromatase inhibitor (AI)-associated bone loss increases fracture rates. Vitamin D might play a role in minimizing this fracture risk. We sought to assess the association between 25-hydroxy-Vitamin D concentrations ([25(OH)D]) at baseline, after 3-months of supplementation, and bone loss after 1 year on AI therapy. Additionally, we investigated the relationship between [25(OH)D] increments ([25(OH)D] at 3 months minus baseline) and AI-associated bone loss. METHODS: Prospective cohort study including a consecutive women initiating AIs for early breast cancer from January/2006 to June/2009 (N=230). Serum [25(OH)D] was measured at baseline and at 3 months, and bone loss was defined as: lumbar spine (LS) absolute loss (baseline minus 1-year BMD) and bone loss rate (absolute loss over baseline BMD). Participants were supplemented with daily oral calcium (1g) and vitamin D3 (800 IU) and, in those with baseline [25(OH)D] was <30 ng/ml,with additional oral 16,000 IU every 2 weeks if. Linear regression models were fitted to adjust for potential confounders. For the current analyses, we included those whithout basal osteoporosis and, hence, not eligible for bisphosphonate therapy. RESULTS: In the overall population (N=156), increasing levels of [25(OH)D] at 3 months were inversely correlated to LS bone loss rates (adjusted beta for each 10ng/ml -0.41 [95%CI - 0.68 to -0.13], p=0.005) and to absolute bone loss (-0.004 g/cm2, [-0.007 to -0.004], p=0.003) at 1 year. [25(OH)D] increments at 3 months were also protective (adjusted beta for each 10 ng/ml for bone loss rates: -0.46 [-0.71 to -0.21], p<0.001; for absolute bone loss: -0.004 [-0.007 to -0.002], p<0.001). Of note, in the subset with baseline deficiency, baseline [25(OH)D] appeared directly related with BMD loss, although this was of borderline significance (adjusted beta for each 10 ng/ml 1.1, 95%CI -0.008 to 2.25, p-val 0.07). CONCLUSIONS: [25(OH)D] increments due to supplementation prevents AI-associated bone loss, independently of baseline [25(OH)D]. Hence, vitamin D supplements, with higher dosage than the standard 400 to 800 IU/day, might be useful to minimize bone loss in low risk women starting on AIs.