We are taller in the morning because our spines lengthen while sleeping. The vertebrae in our spine are separated by elastic discs that relax and stretch overnight when our body weight is not bearing down. This allows us to grow about 1 cm taller. However, during the day the discs compress under our weight, so we shrink slightly by evening. Ensuring proper sleep and a supportive mattress allows our spines to fully relax and lengthen overnight.