British Medical Journal Open. 9:e029046.
Reviewing numerous studies involving children, adults, and prenatal exposure, the authors concluded that consumption of soft drinks is associated with significantly increased odds of asthma in both adults and children, as well as marginally significant in prenatal exposure.
They mentioned that sugar activates an inflammatory pathway and that additives in soft drinks may trigger symptoms. They specifically noted sodium benzoate and sulfites as examples, but did not mention that some of the food dyes commonly present in soft drinks have been known to be bronchoconstrictors since the 1980s. They did, however, say that at this time it is not known whether any of these substances specifically are involved in the actual development of asthma in spite of being known to trigger attacks in a person who has it.