My grandmother smoked for decades, and although she did eventually succeed in quitting, she still spent the last few years of her life linked to an oxygen tank. And as a medical journalist, I’m very familiar with the long list of health-related disadvantages of smoking. So you can’t blame me for being skeptical when I learned that smoking might actually have a protective effect against osteoarthritis (OA).
As counterintuitive as it may seem, a 2011 meta-analysis of 48 studies found an inverse relationship between smoking and OA of the knee and hip, and more research suggesting this protective effect has been published since then. Research has also found smoking to be protective against ulcerative colitis and Parkinson disease, possibly due to stimulatory effects of nicotine on neuronal acetylcholine receptors.
But, as we all know, study findings are not always as they seem. And the most recent publications on this topic suggest the relationship between smoking and OA is actually quite complicated.
As clinicians familiar with the biomechanics of OA in weightbearing joints, you might rightly point out that lower body mass index (BMI) in smokers than nonsmokers would naturally be associated with a lower risk of OA. But, although the aforementioned meta-analysis found the apparent protective effect of smoking was greater when the authors did not control for BMI, the positive effect still persisted after BMI was accounted for.
And the association between thinness and an apparent protective effect of smoking on OA risk may actually be important. In a March 2015 editorial, OA researchers from Boston University noted that variables other than smoking status (genetics, for example) can contribute to thinness, and the interaction between smoking and one or more of those other variables may underlie any protective effect.
It should also be noted that multiple OA studies have not found a protective effect of smoking. That includes a University of Massachusetts study epublished in late September in which smoking status was not associated with longitudinal changes in OA symptoms or joint space width.
Even more interesting from a clinical perspective is that, while the 2011 meta-analysis did find that smokers had less severe radiographic OA than nonsmokers, smokers had more severe OA pain than nonsmokers. That’s the finding that really hits home for me.
For my brother’s most recent birthday, he asked for a vapor-based electronic cigarette system to help him give up smoking as part of an ongoing commitment to a healthier lifestyle. Interestingly, he’s also had significant knee OA pain for most of his adult life.
It would take a lot for me to discourage my brother–or anyone–from quitting smoking. Nobody in our family wants to see my brother go through what our grandmother went through at the end of her life, and, even if giving up cigarettes ultimately increases the progression of radiographic knee OA, that’s a trade I would always be willing to make. But, if giving up cigarettes can also help to alleviate my brother’s knee pain, that’s yet another good reason to do it.