Boursiquot BC, et al. - In a secondary analysis of the Women’s Health Initiative (WHI) trial on calcium and vitamin D (CaD) supplementation vs placebo, researchers investigated the efficacy of CaD supplementation for atrial fibrillation (AF) prevention for the first time. They identified 1,453 (8.6%) cases of incident AF over an average of 4.5 years among 16,801 included participants, at an average rate of 19.9 events per 1,000 person-years. CaD was found to have no effect on AF incidence, and baseline serum 25(OH)D level was not identified to be predictive of long-term incident AF risk in WHI CaD trial participants.