Did you manage to get the confidence intervals for those odds estimates? My
field is not LBP but the smoking literature does interest me.

The full text reports of those studies might indicate whether any
confounding variables are likely to have influenced the effect estimates (if
they don’t report these then the paper is suspect).  If they do,
multivariate regression analyses or stratified analyses might reveal more
detail and allow judgement of cause and effect, say using Bradford-Hill
criteria. This is particularly relevant if the estimates haven’t been
adjusted for age given Deyo’s observations on increase in effect with
smoking pack years.

In terms of the magnitude of effect, OR’s in the range you report are in
general pretty good evidence of effect (providing CI’s don’t cross 1 and the
trials are adequately powered). However, with smoking because cause and
effect is so controversial (i.e. the tobacco companies lawyers don’t like
you saying that it’s causal) most look for an OR of a really large
magnitude. Of course this, like you said, is up for debate!

Doll and Hill, Richard Peto, and Geoffrey Rose’s work has set the ‘tone’ in
terms of risk-effect levels of the multiplicative risk of smoking. For
instance: a non-smoking person not exposed to asbestos has a relative risk
of 1 for lung cancer mortality, a smoking non-exposed person has a RR of
10.9, a non-smoking exposed has a RR of 5.2 and a individual smoker exposed
to asbestos has RR of 53.2 (see Rose, The strategy of preventative medicine,
Oxford, OUP, 1992).

I would be interested to hear if you ever do find evidence on the "impeded
nutrition to the disk" theory. It certainly has biological plausibility.

Alistair Grant
University of Cambridge


>From: Jason Steffe <[log in to unmask]>
>Reply-To: - for physiotherapists in education and practice
><[log in to unmask]>
>To: [log in to unmask]
>Subject: Re: why is sitting bad??
>Date: Sat, 28 Jul 2001 09:37:26 -0400
>
>Frank,
>
>Thanks for the informed and thoughtful reply.  You are obviously well-read.
>
>I came across a couple of studies after searching medline that had a bit
>higher odds ratio (2.33- 2.4, one study had  5.53), but most of the
>abstracts I reviewed were about 1.5 or less.  What a relevant odds ratio
>may be is up to debate, however the trend found by Richard Deyo and a few
>others is that odds ratios increase with increasing pack-years.  I do agree
>that the increased risk for development of LBP isn't as high as the hype
>would have you to believe (OR for CAD are much higher if memory serves),
>but I can't get the "impeded nutrition to the disk" argument out of my
>head.
>
>Some references for those who are interested:
>
>1. Smoking. A risk factor for development of low back pain in adolescents.
>Feldman DE, Rossignol M, Shrier I, Abenhaim L.  Spine 1999 Dec 1;
>24(23):2492-6
>2.Lifestyle and low-back pain. The influence of smoking and obesity. Deyo
>RA. Bass JE.  Spine 1989 May; 14(5):501-6
>3.Eriksen W, Natvig B, Bruusgaard D. Smoking, heavy physical work and low
>back pain: a four-year prospective study.  Occup Med (Lond) 1999
>Apr;49(3):155-60
>4.Scott SC, Goldberg MS, Mayo NE, Stock SR, Poitras B.  The association
>between cigarette smoking and back pain in adults.  Spine 1999 Jun
>1;24(11):1090-8
>
>The material on maintaining lordosis while sitting is very interesting to
>me.  It's nice to finally have some strong evidence for an intervention
>that we commonly utilize for a change.
>
>Regards.
>
>--------------------------------------------
>Jason Steffe, PT, MS, MTC
>Physiotherapy Associates
>1901 Phoenix Blvd, Suite 205
>College Park, GA. 30349
>Ph: 770-907-1023
>Fax:770-907-5608
>   ----- Original Message -----
>   From: Frank Conijn
>   To: [log in to unmask]
>   Sent: Friday, July 27, 2001 1:37 PM
>   Subject: Re: why is sitting bad??
>
>
>   Dear Jason,
>
>   How about the difference between sitting unsupported versus supported
>with a
>   lumbar roll?
>
>   It has been demonstrated that in case of radiating lumbar complaints in
>   young to middle-aged adults, a substantial centralization is achieved
>   through sitting with a roll, while sitting without it caused
>   peripherilization (Williams MM, Hawley JA, McKenzie RA, et al. A
>comparison
>   of the effects of two sitting postures on back and referred pain. Spine,
>   1991;1185-1191).
>
>   >From this study one would conclude that sitting itself is not harmful,
>but
>   wrong ways of sitting are.
>
>
>   Smoking does a have a negative influence, as has been shown
>   (http://www.slackinc.com/bone/ortoday/200105/smoke.asp), but:
>   * should we be impressed with an RR of 1.25-1.85 for smokers? I don't
>think
>   so;
>   * is it the smoking itself, or do smokers (also) have a lower level of
>   exercise/physical activity, causing the increased incidence of LBP?
>
>   The latter could easily be improved (quality and quantity), but to quit
>   smoking is easier said than done....
>
>
>
>   For those with a special interest in sitting (and an over amount of
>   time.......), some more references:
>
>   1. Andersson GBJ, et al: "The sitting posture: An electromyographic and
>   discometric study." Orth Clin North Am. 6 (1): 105-120, 1975.
>   2. Andersson GBJ, Murphy RW, et al: The influence of back rest
>inclination
>   and lumbar support on lumbar lordosis. Spine, 1979,4;1:52-58.
>   3. Bendix T, Biering-Sorenson F: "Posture of the trunk when sitting on
>   forward inclining seats." Scand J Rehab Med 15:197-203, 1983.
>   4. Black KM, McClure P, Polansky M:The influence of different sitting
>   positions on cervical and lumbar posture. Spine, 1996,21;1:65-70
>   5. Harms Ringdahl K:On assessment of schoulder exercise and load-elicted
>   pain in the cervical spine. Scand J Rehab Med Suppl 14, 1986
>   6. Hedman T P,. Fernie G R: Mechanical Response of the Lumbar Spine to
>   Seated Postural Loads. Spine 1997;22;7:734-743
>   7. Lord MJ, Small JM Dinsay JM: Lumbar lordosis. Effects of sitting and
>   standing, Spine, 1997,22;21:2571-74
>   8. Mandal AC: "The correct height of school furniture." Physiotherapy
>   70(2):48-53, 1984.
>   9. Nachemson A: "The load on lumbar discs in different positions of the
>   body." Clin Orthop 35: 107-122, 1966.
>
>   (With thanks to Nico de Bruïne, PT/MT/dipl. MDT, The Netherlands.)
>
>
>   The general conclusion is that sitting with a lumbar kyphosis has a
>   substantial negative influence on lumbar (disc) biomechanics/lumbar
>   complaints (note that most investigations looked at the relatively
>young,
>   let's say under 60-70, which is important since the elderly sometimes
>suffer
>   from a neurogenic claudication with radiation, which can be caused by an
>   osteophytical lumbar stenosis; this would then show an opposite reaction
>to
>   sitting with a lumbar roll).
>
>
>   R.,
>   Frank
>
>
>
>   ----- Original Message -----
>   From: "Jason Steffe" <[log in to unmask]>
>   To: <[log in to unmask]>
>   Sent: vrijdag 27 juli 2001 0:02
>   Subject: Re: why is sitting bad??
>
>
>   Biomechanically speaking, the sitting position (flexion) causes
>hydrostatic
>   pressure which forces the nucleus pulposus posteriorly, against an
>already
>   relatively thin outer and inner annulus.  The outer annulus is drawn
>taut
>   with this position which results in creep over time.  These factors
>combined
>   can cause a problem, especially in individuals with prior discal history
>and
>   deconditioning.
>
>   I agree that sitting itself isn't the culprit.  In my personal view,
>it's
>   prolonged sitting without taking standing breaks to give the tissue a
>   "break", poor physical conditioning, insufficient treatment after prior
>   episodes of LBP (multifidi are still inactive) and smoking.
>   --------------------------------------------
>   Jason Steffe, PT, MS, MTC
>   Physiotherapy Associates
>   1901 Phoenix Blvd, Suite 205
>   College Park, GA. 30349
>   Ph: 770-907-1023
>   Fax:770-907-5608
>


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