There’s no scientific evidence that wearing a bra to bed is either helpful or harmful. It doesn’t prevent your breasts from growing nor does it make your breasts saggy. If you have large breasts (Ex. D, DD or higher) wearing a sports bra to bed may be more comfortable because it will support your breasts, but it’s not necessary. In general, be sure that your bra fits well and isn’t too tight. It’s important to wear a bra that fits well whether you wear it during the day, at bedtime, or both. Sagging of the breasts can happen with pregnancy, breast feeding, gravity, and time.