Respiratory symptoms and bronchial responsiveness are related to dietary salt intake and urinary potassium excretion in male children

To investigate whether dietary salt intake and urinary sodium and potassium levels are related to respiratory symptoms and bronchial responsiveness, a cross-sectional study among 2593 subjects aged 9 to 16 was conducted in four communities of the Latium region (Italy). Questionnaires were administered to the parents, urine samples were collected, lung function, methacholine challenge tests and prick tests were performed. Information about familial and personal dietary salt use and respiratory health was collected from the parents of 2439 (94%) subjects. A total of 2020 methacholine challenge tests and 916 urinary sodium and potassium levels were available for analysis. Personal table salt use was strongly related to cough and phlegm apart from colds (adjusted odds ratios, OR, 1.87, 95% confidence intervals, CI, 1.20-2.90), wheezing apart from colds (OR, 2.19, 95% CI, 1.27-3.77), wheezing with dyspnoea (OR, 1.45, 95% CI, 0.98-2.12) and wheezing after exercise (OR, 2.16, 95% CI, 1.35-3.44). These associations were mainly found in boys. Use of familial table salt and canned food showed no relation to respiratory symptoms. Increased bronchial responsiveness was associated with a higher urinary potassium excretion in boys, but not with urinary sodium. In conclusion, personal table salt use is related to an increased prevalence of bronchial symptoms; an increase in bronchial responsiveness among those with higher potassium excretion also seems to be implied. Although it is difficult to interpret the results of this study in causal terms, the findings might be relevant to the distribution of bronchial symptoms and diseases in the population.