Does less salt = less asthma?
This study hopes to answer this question. I assume, but don't know there is pre-clinical data supporting the salt/asthma link.
One problem with these kinds of studies is how hard it is to get people to actually follow a restricted diet. If humans were good at that type of thing there wouldn't be so much obesity.
UPDATE: Need to look before posting. There is even a Cochrane Review on the topic, which concludes
Based on currently available evidence it is not possible to conclude whether dietary salt reduction has any place in the treatment or management of asthma. The results of this review do indicate an improvement in pulmonary function with low salt diet, however further large scales trials are required before any firm conclusions can be reach.