In 2018, DC Comics published "Anatomy of a Metahuman," a dossier compiled by Batman of twelve characters from the DC universe, from Aquaman and Swamp Thing to Doomsday and Superman himself. The book shows detailed drawings of their internal workings and — for Superman in particular — descriptions of how some of his superpowers work, such as his X-ray vision. Many of Superman's powers are simply a product of his adaptation to the weaker gravity of Earth when compared to his home planet of Krypton, like his ability to leap great distances, giving the illusion of flight.
In a thread on the r/AskScienceFiction subreddit, u/RobotFolkSinger observed that Superman had to make necessary social and biological adaptations to survive when he came from Krypton to Earth as a child. "He doesn't need to breathe as long as there's a yellow sun around," they wrote. "Superman can draw energy directly from the radiation of a yellow sun, so he doesn't need to take in oxygen. He probably still does breathe when on Earth, though, so that the people around him don't notice he isn't and get weirded out."
Some users noted his ability to store and discharge massive amounts of air in his lungs. At the same time, fans seem divided on Superman's biological need to breathe like an ordinary human does.At least one user is convinced Superman has to take in oxygen like any native Earthling. According to u/vadergeek, "He needs to breathe, but he can hold his breath for a ludicrously long period of time." Perhaps writer and director James Gunn will provide fans with some more answers regarding Superman's physiology in "Superman: Legacy" when the film lands in theaters.
