Chronic respiratory symptoms, bronchial responsiveness and dietary sodium and potassium: a population-based study

A possible relationship between Na+ intake and increased prevalence and mortality from asthma and chronic obstructive pulmonary disease (COPD) has been suggested but not clearly proven for several reasons (difficulty in assessing Na+ and K+ both by 24 h excretion and dietary recall, too small an effect of these ions on the pathology, and the role of potential confounders). We wanted to determine the relationship of Na+ and K+ intake, assessed by means of a 7 day recall, with chronic respiratory symptoms and bronchial responsiveness in a sample of the general population. Two hundred and five subjects were studied, with complete dietary and respiratory questionnaires, and baseline respiratory function tests, together with a subsample of 146 subjects who underwent histamine challenge. The 7 day recall consisted of two parts: the first assessed discretionary Na+; and the second assessed Na+ and K+ contained in food. The whole sample was split into two groups based on the levels of consumption, and the statistical analysis was performed contrasting the three lower quartiles vs the highest. Smoking habit, social economic status, age and body mass index (BMI) were not confounders for Na+ and K+ intake. The prevalence of symptomatic subjects and baseline respiratory function values were not significantly different in the two groups of quartiles for Na+ and K+. Baseline respiratory values and dose-response slope of the subsample were also not significantly different. We did not prove a relationship between these dietary factors and either bronchial responsiveness or chronic respiratory symptoms. Although we consider that our questionnaire is more reliable than other methods for Na+ and K+ assessment, several potential biases still remain.(ABSTRACT TRUNCATED AT 250 WORDS)