The smoking ban in public places has been linked to 1,900 fewer emergency hospital admissions for asthma patients every year, researchers have found.
The ban, which came into force in England in July 2007, has been associated with an annual 5% drop in adult admissions, they said.
Researchers from the University of Bath examined the number of emergency admissions during the first three years after the ban on smoking in public places was introduced in England - where the prevalence of asthma is one of the highest in the world, affecting almost 5.9% of the population.
The study, published in the journal Thorax, looked at the 502,000 emergency admissions for asthma among adults aged 16 and over in England between April 1997 and December 2010.
After taking account of seasonal temperatures, variations in population size, and long-term trends in the prevalence of asthma, the figures showed that emergency admissions for the condition fell by 4.9% among adults for each of the first three years following the introduction of the smoking ban. The decrease was found to be consistent across the country.
Smoking laws introduced in other countries have been linked with up to 40% reductions in the number of emergency asthma admissions.
The authors said that although the 5% drop is lower than decreases noted in other countries, this might be because many workplaces in England had already adopted smoke free policies before the nationwide ban took effect.
"(The study) provides further support to a growing body of national and international evidence of the positive effects that introducing smoke free policies has on public health," the authors said. But they cautioned that while the association they found was significant, it does not prove that the legislation was responsible for the fall in emergency admissions for asthma.
Emily Humphreys, head of policy and public affairs at charity Asthma UK, said: "Eight out of 10 people with asthma tell us that other people's smoke makes their asthma worse.
"That's why we campaigned for the smoke-free laws and are delighted to see evidence of the benefits these are having on the millions of people with asthma in England. By taking action to reduce asthma triggers, we can prevent asthma attacks that can lead to hospitalisation and even death. However, more still needs to be done to prevent attacks, which kill three people each day in the UK."