You should wear a bra to bed if it makes you feel comfortable. Wearing it to sleep offers no concrete health benefits and does not prevent breast sagging as of 2014.
Wearing a bra to bed does not stop breasts from drooping and does not reverse sagging. Women with heavy breasts may benefit from choosing to wear one to sleep, as the additional support keeps them comfortable. It is important for pregnant and lactating women to wear a bra with nursing pads to bed, as this prevents milk stains on clothing and protects further irritation to tender breasts. According to studies published in the journal Cancer Epidemiology, Biomarkers & Prevention, there is no association between wearing a bra to sleep and the risk of breast cancer among post-menopausal women.
Sleep bras are meant to be worn to bed. They are soft, provide less support than regular bras and are fashioned for women of all body types. Wearing sleep bras under loose-fitting nightwear enhances your level of comfort, can prevent stretch marks and may help slow down the aging process.
Women with breast implants can wear a bra to bed to reduce discomfort. Wearing a bra with an underwire during sleep can cause breast irritation and may interfere with the quality of sleep. Specially designed bras, when worn to bed, may prevent cleavage wrinkles.