Dietary vitamin C intake is inversely related to cough and wheeze in young smokers

We aimed to investigate whether dietary vitamin C intake, an important antioxidant, is inversely related to self-reported respiratory symptoms in young adults of a community. A random sample of 4300 subjects, aged 20 - 44 years, living in Bergen, Norway, received a postal questionnaire on respiratory symptoms; 80% responded. Vitamin C intake (mg per week) was estimated from a food-frequency questionnaire asking how often the subject, during the last year, had consumed units of orange juice, oranges, potatoes, carrots and tomatoes. Significant differences in the intake of vitamin C were observed across smoking categories with current smokers having the lowest intake, while there was no variation by gender, age or occupational dust exposure. Dietary vitamin C intake was in univariate analyses inversely related to "morning cough", "chronic cough", "wheeze" and "wheeze ever". After adjusting for gender, age, body mass index, "occupational exposure" pack-years as well as having and stratified on smoking habits in multiple logistic regression analyses, the relationship between dietary vitamin C intake and "cough" and "wheeze" tended to be associated to smoking. The odds ratio (OR) for "morning cough" was 0.68 (95% CI: 0.35-0.95), "chronic cough" OR 0.69 (95% CI: 047-1.04) and "wheeze ever" OR 0.75 (95% CI: 0.56-1.01) in current-smokers with dietary vitamin C intake in the upper (≥395 mg/week) vs. the lower (< 209 mg/week) tertile. The OR for "wheeze" was 0.56 (95% CI: 0.35-0.88) in ex-smokers.The magnitude of these effects remained after excluding subjects with supplementary vitamin C intake (n= 199) from the statistical analyses. Among young Norwegian adults, having a low prevalence of asthma and high prevalences of smoking-related respiratory symptoms, dietary vitamin C intake may act as an antioxidant and thereby reduce cough and wheeze in smokers having high oxidant stress.