The research led by Catalan Institute of Oncology researchers showed that 5pct of the waiters stopped smoking, and the number of cigarettes smoked by those who still smoke has fallen by almost 9pct.
The law banning smoking in public places was brought force on January 1 2006.
Within 3 years, the proportion of smokers strongly addicted to nicotine has halved as a result of the law.
All the effects observed during this research study, have been "significantly reduced" among waiters in bars where smoking has been completely banned than among those who work in places with smoking areas, or where there are no restrictions in place.
"Changing the partial ban on tobacco consumption in bars and restaurants for a total ban would have beneficial effects on the health of all the workers in this sector", Esteve Fernandez, one of the authors of the study and a researcher at the ICO, told SINC.
In addition, levels of cotinine - a nicotine metabolite used to measure active, and especially passive, exposure to smoke - in the workers' saliva also fell by 4.4pct.
The study is published in the journal Nicotine and Tobacco Research.