Researchers found that people who smoke may be much more likely to develop chronic back pain, as the habit reduces their resilience to it.
This is not the first study to link smoking to chronic pain. But according to the research team, led by Bogdan Petre of the Feinberg School of Medicine at Northwestern, it is the first study to suggest that smoking interferes with a brain circuit associated with pain, making smokers more prone to chronic back pain.
Back pain is one of the most common medical problems in the US, estimated to affect 8 out of 10 Americans at some point in their lives. According to the American Chiropractic Association, back pain is the main reason for missed days at work and the second most common reason for doctor's visits.
This latest study, published in the journal Human Brain Mapping, suggests that smokers could reduce their risk of developing chronic back pain by quitting the habit.
To reach their findings, the researchers analyzed 160 participants who had recently developed subacute back pain, defined as back pain lasting 4-12 weeks. They also assessed 32 participants with chronic back pain - defined as having back pain for 5 years or more - and 35 participants with no back pain.
On five separate occasions over a 1-year period, all participants completed questionnaires that gathered information about their smoking status and other health conditions. They also underwent magnetic resonance imaging (MRI) brain scans.
The brain scans, the researchers say, were used to assess activity between two brain regions - the nucleus accumbens and the medial prefrontal cortex. Both of these regions play a role in addictive behavior and motivated learning.
Smoking increases brain activity that reduces resilience to chronic back pain
Petre and his team found that the connection between these two brain regions plays a crucial role in chronic pain development. They explain that the stronger the connection between them, the less resilient an individual is to chronic pain.
Smoking appears to affect this connection. The researchers found that compared with nonsmoking participants, those who smoked had a stronger connection between the nucleus accumbens and the medial prefrontal cortex, increasing their risk of chronic back pain. The team calculated that smokers are three times more likely to develop chronic back pain than nonsmokers.
"But we saw a dramatic drop in this circuit's activity in smokers who - of their own will - quit smoking during the study," explains Petre. "So when they stopped smoking, their vulnerability to chronic pain also decreased."
Commenting on their findings, the researchers say:
"We conclude that smoking increases risk of transitioning to chronic back pain, an effect mediated by corticostriatal circuitry involved in addictive behavior and motivated learning."
The team points out that smoking participants who managed their chronic back pain with medication - such as anti-inflammatory drugs - did experience some pain reduction, but that these medications did not alter brain circuitry.
As such, they suggest that smokers could reduce their risk of chronic back pain by engaging in smoking cessation programs or other behavioral interventions that may help them quit the habit.
Because the team's findings show that smoking affects brain circuitry linked to chronic pain, they suggest that there may be a link between addiction and chronic pain in general.
Last month, Medical News Today reported on a study published in JAMA Internal Medicine suggesting that around 14 million major medical conditions in the US are attributable to smoking.