I read a magazine article saying McKenzie exercises are the answer to low back pain. Six months later and I'm still in pain.

The exact mechanism by which smoking affects the muscles, bones, and other tissues of the body is still unknown. It may be that smoking speeds up bone loss at the cellular level. This kind of change causes backbone deformities and loss of stability in the spine. It could also be that smoking affects the metabolism of the disc between the bones in the spine. This could lead to disc degeneration.

Another theory is that smoking affects blood vessels and reduces blood supply to the spine. Without enough blood, the bones and tissues don't get enough nutrition. Back pain could also be intensified by the effects of smoking on the nervous and hormonal systems.