Jip, its a known association, any helicopter pilot with more than 1000 hours is likely to have some form of back problem, due to the maintained rotated posture of the upper body. Sitting slightly forward and rotated to the left, due to the right hand on the cyclic and the left on the collective, as well as the assymmetry of the pedal inputs, apparently places unusual strain on the lower back, especially in those individuals who are not physically active. With age, lower back problems become increasingly common anyway, spondylosis and disc pathology in particular. Continued postural aggravation like in a helicopter may very well worsen things. Hope there are some orthopods out there to comment?
http://www.flightsafety.org/hf/hf_may-june00.pdf