Objective: To examine the cross sectional relationship between respiratory function and plasma vitamin C.
Design: Cross sectional analysis.
Setting: Population based study.
Subjects: 835 Men and 1025 women aged 45 to 75 registered with GP practices in Norfolk.
Interventions: Completion of health and lifestyle questionnaire and attendance for a health check.
Main outcome measures: Forced expiratory volume in one second (FEV1), forced vital capacity (FVC) and non fasting plasma vitamin C.
Results: Plasma vitamin C was positively correlated, after adjustment for age and height, with both FEV1 (r = 0.17, P < 0.001) and FVC (r = 0.14, p < 0.001) in men. The association in women was weaker and not statistically significant. Adjusting for other possible factors and exclusion of various groups did not alter the observed associations. The differences in FEV1 and FVC in men, adjusted for age, height and cigarette smoking, for a 50 micromol/L difference in vitamin C were 0.22 litres (95% CI 0.10-0.33) and 0.23 litres (95% CI 0.09-0.37) respectively. The population distribution was shifted such that 12.1% of men with vitamin C levels < or = 30 micromol/L had an FEV1 of less than two litres, compared with 4.6% with levels > or = 60 micromol/L.
Conclusions: These findings are consistent with other studies of vitamin C and respiratory function and suggest that vitamin C may be protective for lung function through the whole normal range of dietary intake and lung function.