Effects of vitamin C on airway responsiveness to inhaled histamine in heavy smokers

Abstract

Histamine bronchial threshold, the provocation concentration of histamine causing a 25% fall in maximal expiratory flow at 50% of forced vital capacity from the control value (PC25MEF50), was measured in seven heavy smokers and in seven sex- and age-matched nonsmokers before and one hour after ingestion, double-blind, of vitamin C (2 g) or placebo. Smokers had significantly lower baseline values of serum ascorbate, maximal expiratory flow at 50% of forced vital capacity (MEF50) and PC25MEF50: the latter was negatively related to serum ascorbate (r = -0.85; p < 0.001). Acute treatment with vitamin C produced a significant decrease in PC25MEF50 in smokers (95% confidence limit (CL) from 4.87-3.36 to 2.91-2.01 mg·ml-1; p = 0.017), whilst it had no effect in nonsmokers. A preliminary open study on the effect of prolonged administration of vitamin C (1 g daily) was performed in smokers. One week of treatment produced a further significant decrease in PC25MEF50 (p < 0.0001). Our results suggest that in heavy smokers histamine bronchial responsiveness may be attenuated by chronic ascorbate deficiency. In these circumstances, acute and short-term treatment with vitamin C may increase the bronchoconstrictive response to inhaled histamine.