Smoking has been linked to earning less and having a harder time finding jobs, according to a new study.

Researchers from Stanford University found that smokers remain unemployed for longer and earn substantially less than their nonsmoking counterparts when they do find jobs.

Previous studies on populations in the United States and Europe have already linked smoking to unemployment, and lead researcher Judith Prochaska and her team previously found that unemployed job seekers in California were significantly more likely to be smokers. However, researchers wanted to understand whether smoking was the cause or effect of unemployment.

"You don't know if smokers have a harder time finding work or if smokers are more likely to lose their jobs - or that when nonsmokers lose their jobs, they become stressed and start to smoke," said Prochaska, an associate professor of medicine at Stanford University Medical Center.

For the latest study, researchers surveyed 131 unemployed smokers and 120 unemployed nonsmokers at the beginning of the study, at six months and at 12 months.

"We found that smokers had a much harder time finding work than nonsmokers," said Prochaska.

The year-long study revealed that only 27 percent of smokers had found jobs compared with 56 percent of nonsmokers at the end of the study, and smokers who found jobs by 12 months earned on average $5 less per hour than their nonsmoking counterparts.

"The health harms of smoking have been established for decades, and our study here provides insight into the financial harms of smoking both in terms of lower re-employment success and lower wages," Prochaska added.

Researchers used survey answers and breath test results to group job seekers into either daily smokers or nonsmokers. Prochaska and her team noted that smokers in the study were on average younger, less educated and in poorer health than nonsmokers.

"We designed this study's analyses so that the smokers and nonsmokers were as similar as possible in terms of the information we had on their employment records and prospects for employment at baseline," said Michael Baiocchi, an assistant professor of medicine at Stanford University Medical Center, who co-authored the study.

The findings were published in the journal JAMA Internal Medicine.