Back pain can also be caused by smoking. The disks between the vertebrae are filled with fluid. During the day, the fluid is slowly squeezed out and they get flat. During the night when you're lying down, the pressure is off of them and they reabsorb fluid and swell back up again.
Smoking leaves chemicals in the body that coat the disks and prevent them from absorbing the fluid. They don't swell up at night and the result is pain the next day.
