The study, published in The Journal of the American Medical Association, comes from Scotland, which banned smoking in bars and other confined public places on March 26, 2006.
The ban presented a golden opportunity for researchers including Daniel Menzies, MBChB, of Ninewells Hospital and Medical School in Dundee, Scotland.
Menzies' team studied 77 nonsmoking bar workers in Tayside, Scotland, before and after the ban went into effect.
The bar workers completed questionnaires about their lung symptoms. They also took lung function tests and provided blood samples for the study.
Before the ban, nearly 80 percent of the bar workers reported having lung symptoms such as wheeze, shortness of breath, cough, and phlegm.
One month after the ban, that percentage dropped to about 53 percent and fell even further to 47 percent in the second month.
The bar workers' lung function also improved and they had lower levels of cotinine in their blood after the ban began. Cotinine is a measure of exposure to tobacco smoke.
The 12 bar workers with asthma also reported better quality of life after the ban, the researchers report.
The study "confirms and amplifies previous research" on the lung effects of smoking bans for restaurant and bar workers, writes editorialist Mark Eisner, MD, MPH.
Eisner works at the University of California, San Francisco. He wasn't involved in the Scottish study.
There is "compelling scientific evidence that smoke-free workplace legislation is rapidly effective in improving the health of workers," Eisner writes, adding that "the time has come to clear the air."
SOURCES: Menzies, D. The Journal of the American Medical Association, Oct. 11, 2006; vol 296: pp 1742-1748. Eisner, M. The Journal of the American Medical Association, Oct. 11, 2006; vol 296: pp 1778-1779. News release, JAMA/Archives.
By Miranda Hitti
Reviewed by Louise Chang