Wood ME, Liu H, Storrick E, et al. - This multicenter randomized controlled trial was used to evaluate the impact of one year of vitamin D supplementation on mammographic density (MD), a biomarker of breast cancer risk. Researchers randomized premenopausal women with > 25% MD and no history of cancer into 2,000IU of vitamin D or placebo orally daily for 1 year. Using Cumulus software, change in percent MD was investigated after all participants completed treatment. They included a total of 300 women between January 2011 and December 2013 with a mean age of 43 and diverse ethnicity (14% Hispanic, 12% African American). A significant improvement was observed in vitamin D levels with 2,000 IU for one year, with 100% of supplemented women achieving sufficiency. Nevertheless, they found a null effect regarding the change in MD for premenopausal women (the primary outcome of the study).