(This August 3rd story has been refiled to add dropped “of” to headline)

Reuters Health - Lifestyle factors like obesity and smoking are known to raise people’s risk of developing sciatica, but a new study finds that regular walking and biking may have an opposite, and just as powerful effect.

Researchers in Finland analyzed data on more than 35,000 people in that country who were followed for up to 30 years, and found that smoking and obesity each raised the risk of being hospitalized for sciatica by 33 percent or more, while regularly commuting on foot or by bicycle lowered the risk by 33 percent.

“The harmful effects of overweight, obesity and smoking, and the protective effect of walking or cycling to work on hospitalization are substantial,” said lead study author Dr. Rahman Shiri of the Finnish Institute of Occupational Health in Helsinki.

“These findings have important implications for prevention,” he told Reuters Health by email.

About 2 to 5 percent of people have sciatica, the authors note in the American Journal of Medicine. The painful condition typically results from a herniated disc in the lower back and a compressed nerve root, with shooting pain from the lower back along the sciatic nerve that extends down the back of the thighs and legs.

Sciatica rarely leads to surgery or hospitalization, but it’s considered one of the more long-lasting and severe low back pain syndromes, Shiri said.

The study team analyzed data from four long-term studies with a total of 34,589 participants and 1,259 hospitalizations for sciatica during 12-30 years of follow-up. They looked at risk factors such as smoking, body mass index, obesity, age, sex, education and occupation, as well as the frequency, intensity and duration of physical activity.

Although smoking increased the risk of hospitalization for sciatica by 33 percent, former smokers were not at increased risk. Obesity increased hospitalization risk by 36 percent, especially abdominal fat, which pushed the increase to 41 percent.

At the same time, commuting to work by walking or cycling reduced the risk by 33 percent, which was true happened regardless of body weight and other activity.

“Other types of leisure time physical activities had no effect on hospitalization,” Shiri added. “That was somewhat unexpected.”

Regular low-level physical activities such as walking and cycling may be helpful because they don’t strain the lower back, the study authors note, as opposed to higher-intensity exercise that may be harmful.

One limitation of the study is that it relies on self-reported data, and the researchers are unable to verify what other health factors were involved with hospitalization for sciatica. The studies also used different questions about leisure-time physical activity, and two surveys didn’t have enough information to distinguish between potential gender-related differences.

Future studies should analyze long-term data related to these factors and measure the physical activity directly, the study authors write.

“It could be, for example, that there is something else associated with smoking and independently makes people more likely to be admitted to the hospital for sciatica,” said David Coggon, a professor of occupational and environmental medicine at the University of Southampton in the UK.

Perhaps more importantly, future studies should look at the major changes in back pain and sciatica occurrence over time, Coggon added. For example, long-term workplace absence due to low back pain has increased eightfold between the 1950s and 1970s, said Coggon, who wasn’t involved in the study.

“That said, there are plenty of other good reasons not to smoke, not to be obese, and to exercise,” Coggon said. Changing habits could have “practical implications for public health” for many disorders or diseases, he added.

SOURCE: bit.ly/2u8WZFH American Journal of Medicine, online July 24, 2017.