Even before Halle Berry famously announced she sleeps in a bra, the Huffington Post addressed the issue. Dr. Amber Guth, associate professor of surgery and director of the Breast Cancer Surgery Multidisciplinary Fellowship at NYU Langone Medical Center, told the Huffington Post in 2012 that there is absolutely no evidence that it is harmful or helpful.
In the same HuffPo article, Linda Becker, a professional bra fitter, chimed in and said, “Either your breasts are being supported for eight hours, or they’re not being supported for eight hours. What do you think is better? It’s just common sense."
One thing experts agree on is that if you're going to sleep in bra, make sure it's comfortable and not constrictive. Bottom line: it's up to you (and yours) to decide what's right for you.