By Rachael Myers Lowe

NEW YORK, US - If you needed another reason to cut the cigarette habit: Smokers, especially younger smokers, are more likely to report low back pain than people who have never smoked, according to a new analysis.

After examining existing research, Finnish researchers concluded smoking is "modestly" associated with the risk of low back pain and the effects may be "at least partly reversible." Their findings are published in the January issue of the American Journal of Medicine.

Dr. Rahman Shiri of the Finnish Institute of Occupational Health and colleagues wanted to know if smoking increases the risk of low back pain, a problem that affects an estimated 8 in 10 adults during some point in their lives.

Previous analysis of the existing research came to different conclusions, with one study suggesting an association between smoking and low back pain and the other reporting "unclear findings."

The Finnish researchers identified and reviewed 81 studies from around the world involving smokers, former smokers, or never-smokers and low back pain conducted between 1966 and 2009. Of those, 40 studies involving more than 300,000 adults and adolescents met the standards for the analysis.

The Finnish team subjected the data of the individual studies to further statistical analysis to tease out the strength of relationships even as the studies reported various outcomes.

They determined that even though the data did not prove smoking leads to low back pain, the analysis of previous the literature suggested a "fairly modest" association between smoking and low back pain.

"Current smokers (adolescents or adults) are at only 31% higher risk of low back pain compared with never smokers but this estimate is only for low back pain for one day or more during the past 12 months," Shiri told Reuters Health in an email.

The smoking/low back pain association was strongest for "chronic or disabling low back pain" but, Shiri cautioned, none of the studies were designed to determine if there was a cause and effect relationship.

Scientists don't know why smoking may be associated with lower back pain, although there are a number of possible explanations, including reduced blood supply to the spine, increased risk of osteoporosis, and the increased circulation of pain conducting chemicals in the blood from smoking.

The research suggests the young "might be more vulnerable to the effects of smoking than adults" because the low back pain/smoking association was stronger in adolescent smokers than adult smokers. Another explanation, the authors said, may be that it's easier to identify and study true rate of low back pain in young people than in adults.

The research does suggest "the effects of smoking may be at least partially reversible," since former smokers were less likely to seek care for low back pain than current smokers. More research into former smokers will be needed to make a more definitive claim, the authors said.

SOURCE: The American Journal of Medicine, January 2010.