there is an opinion that it is better to sleep without wearing a bra, is that true? what is the reason? Thanks
It may help to know how the bra developed as an undergarment. It dates only to the late-1920s, when women in the UK and US started wearing sleeveless dresses. It caught on more in the 1930s when women started working closely with men outside the home, such as in offices. If you are lactating (producing milk) it's a convenient way to wear nipple shields to avoid wet spots on your clothes) but a bra serves no real health/medical purpose. It's useful for busty women who run or are in athletic competition or training. However, it's real reason was only this: conceal nipple protrusion, and limit bounce when walking. It's sole purpose, therefore, was to reduce men's staring and unwanted attention. There is no health benefit to wearing a bra. Sure, you can find ancient examples in Roman mosaics of women engaged in athletic competition or exercise, but the bra was not commonly worn by women anywhere until the late-1920s. If you don't have large breasts, and you are comfortable without a bra, you should feel free to go braless not just when you sleep but all of the time. My grandmothers, born in 1892 and 1904, respectively, never wore bras until they were well into adulthood - bras didn't exist when they were young adults. One of my grandmothers probably never wore a bra. She lived a good, full life.
Unless it's a country where monitoring people in their bedrooms happens to be a thing, nobody else should know and people can have that comfort. As children I guess most of us were sent to bed with PJs. Perhaps the thought is it helps to stay warm in the event of dislodging the covers overnight. Once I reached teens, I discovered sleep was better without wearing things on my body, and I learned how to navigate covers. There's an additional consideration for boys/men, something happens during sleep and obstructing that process can be uncomfortable, even painful, causing disruption of sleep.