A crucial dietary measure that would reduce the incidence and severity of childhood asthma is to avoid feeding children salty meals and snacks. - See this article, where you will read, "According to a new study published in the American Dietetic Association, high-salt foods and snacks are linked to lung changes that trigger asthma symptoms.," and that researchers in Greece found, using questionnaires, "Kids who ate high-salt foods more than three times a week saw their risk of asthma symptoms go up almost five times."
We read in this Telegraph report of research in Rome, Italy, led by Dr Giuseppe Corbo. "The study of 20,000 six and seven-year-olds, published in the medical journal Epidemiology, confirmed a strong link with asthma and obesity, but found that salt was the biggest risk. Those with the highest intake were two and a half times more likely to develop asthma." (my emphasis) See also Salt/Sodium in Foods.
Another important precaution is to avoid dosing children with paracetamol/acetaminophen (aka Tylenol and Calpol). There is a wealth of statistical data on that webpage which suggests a link between acetaminophen and childhood asthma.
Since AsthmaUK suggested this week that a third of people with asthma are at a high risk of having a potentially fatal asthma attack (see this BBC report), I reckon AsthmaUK ought to do the decent thing and bring these simple precautionary measures to the attention of asthma sufferers and their relatives and carers. Surely it is a moral imperative.