Smoking bans for bars seem to quickly improve the lung health of workers exposed to less second-hand smoke, a new study suggests.

Researchers studied 77 bar workers in Tayside, Scotland, before and after the country banned smoking in bars and confined public places in 2002.

The non-smoking workers participating in the study filled in questionnaires about their lung symptoms, took lung function tests and gave blood samples.

Before the ban, nearly 80 per cent — 61 people — reported respiratory symptoms such as wheezing, shortness of breath, coughing and phlegm or sensory symptoms such as red eyes and a runny nose.

One month after the ban went into effect, the number reporting such symptoms dropped by about a third, to 41 people. The study by Daniel Menzies and colleagues from Ninewells Hospital and Medical School in Dundee, Scotland, appeared in the Journal of the American Medical Association.

The ban "has led to a rapid and marked improvement in the health of bar workers," the researchers concluded. 

After two months of a smoke-free policy, about 47 per cent of participants reported symptoms, down 32 percentage points from when the study began.

The 12 bar workers who had asthma showed less airway inflammation and higher quality of life scores after the ban, the researchers found.

"The comprehensive body of research documenting the serious adverse health effects of passive smoking provides a powerful rationale for prohibiting smoking in all public places," Dr. Mark Eisner of the University of California, San Francisco, wrote in an editorial accompanying the study. "The time has come to clear the air."

The hospitality industry has argued that smoking bans will be ineffective, won't be accepted and will cause bars and restaurants to lose money.

Yet adherence rates have remained high in California, Boston, Ireland and New Zealand.

International studies suggest most people do support smoke-free bars and restaurants, and sales tax and financial data show the businesses do not report lost revenue after going smoke-free, Eisner said.